Hello everyone!
In first, i would like to apologize for my execrable english, but I will try to make efforts !
So, i try to use an autoscroll in a panel with layout=fit but it does not work. Even if i have a lot of child container (which overflow the parent container), it does not work.

I change the text in text aera because it is quite confidential ...

Code:
<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="WebForm2.aspx.cs" Inherits="Dcx.DiagBatiment.WebForm1" %>

<%@ Import Namespace="System.Collections.Generic" %>
<%@ Register Assembly="Ext.Net" Namespace="Ext.Net" TagPrefix="ext" %>
<script runat="server">
</script>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" 
    "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head id="Head1" runat="server">
    <title>Diag</title>
    <link href="../../../../resources/css/examples.css" rel="stylesheet" type="text/css" />
    <style type="text/css">
        .edi
        {
            font: 11px Tahoma;
            text-align: center;
            background-color: Fuchsia;
        }
    </style>
    <script type="text/javascript">
    </script>
</head>
<body>
    <form id="form1" runat="server">
    <ext:ResourceManager ID="ResourceManager1" runat="server" />
    <ext:Viewport runat="server" MonitorResize="true">
        <Items>
                    <ext:Panel runat="server" Title="Tableau1" Frame="true">
                        <TopBar>
                            <ext:Toolbar runat="server">
                                <Items>
                                    <ext:Button runat="server" Text="Ajout" Icon="Add" />
                                    <ext:ToolbarFill runat="server" />
                                    <ext:Button runat="server" Text="RAZ" Icon="Delete" />
                                </Items>
                            </ext:Toolbar>
                        </TopBar>
                        <Items>
                            <ext:Panel ID="Panel1" runat="server" Header="false" frame="true" AutoScroll="true" Width="1000" Layout="fit">
                                <Items>
                                    <ext:Container ID="Container5" runat="server" Layout="hbox">
                                        <Items>
                                            <ext:FormPanel ID="FormPanel1" runat="server" Margins="5 0 0 0">
                                                <Items>
                                                    <ext:Container ID="Container1" runat="server">
                                                        <Defaults>
                                                            <ext:Parameter Name="ReadOnly" Value="True" Mode="Value">
                                                            </ext:Parameter>
                                                            <ext:Parameter Name="Cls" Value="edi" Mode="Value">
                                                            </ext:Parameter>
                                                            <ext:Parameter Name="Selectable" Value="False" Mode="Value">
                                                            </ext:Parameter>
                                                            <ext:Parameter Name="Height" Value="50" Mode="Value">
                                                            </ext:Parameter>
                                                        </Defaults>
                                                        <Items>
                                                            <ext:TextArea ID="TextField1" runat="server" Width="130" Text="Poste 1" />
                                                            <ext:TextArea ID="TextField2" runat="server" Width="80" Text="Besoins " />
                                                            <ext:TextArea ID="TextArea2" runat="server" Width="100" Text="poste 2" />
                                                            <ext:TextArea ID="TextArea3" runat="server" Width="70" Text="Poste 3" />
                                                            <ext:TextArea ID="TextArea4" runat="server" Width="30" Text="Rdt" />
                                                            <ext:TextArea ID="TextArea5" runat="server" Width="30" Text="Rdt D" />
                                                            <ext:TextArea ID="TextArea6" runat="server" Width="30" Text="Rdt E" />
                                                            <ext:TextArea ID="TextArea7" runat="server" Width="40" Text="Rdt R/P" />
                                                            <ext:TextArea ID="TextArea8" runat="server" Width="40" Text="Rdt Stoc" />
                                                            <ext:TextArea ID="TextArea9" runat="server" Width="40" Text="Rdt Gbl" />
                                                        </Items>
                                                    </ext:Container>
                                                    <ext:Container ID="Container2" runat="server" Layout="HBox">
                                                        <Items>
                                                            <ext:TextArea ID="Textfield3" runat="server" Width="590" Height="20" Text="Poste 4"
                                                                ReadOnly="True" Selectable="False" />
                                                        </Items>
                                                    </ext:Container>
                                                    <ext:Container ID="Container4" runat="server" Layout="HBox">
                                                        <Items>
                                                            <ext:TextArea ID="TextArea1" runat="server" Width="590" Height="20" Text="Poste 5"
                                                                ReadOnly="True" Selectable="False" />
                                                        </Items>
                                                    </ext:Container>
                                                    <ext:Container ID="Container6" runat="server" Layout="HBox">
                                                        <Items>
                                                            <ext:TextArea ID="TextArea13" runat="server" Width="590" Height="20" Text="Poste 6"
                                                                ReadOnly="True" Selectable="False" />
                                                        </Items>
                                                    </ext:Container>
                                                </Items>
                                            </ext:FormPanel>
                                            <ext:FormPanel ID="FormPanel3" runat="server" Margins="5 0 0 0" Visible="true">
                                                <Items>
                                                    <ext:Container ID="Container11" runat="server">
                                                        <Defaults>
                                                            <ext:Parameter Name="ReadOnly" Value="True" Mode="Value">
                                                            </ext:Parameter>
                                                            <ext:Parameter Name="Cls" Value="edi" Mode="Value">
                                                            </ext:Parameter>
                                                            <ext:Parameter Name="Selectable" Value="False" Mode="Value">
                                                            </ext:Parameter>
                                                            <ext:Parameter Name="Height" Value="50" Mode="Value">
                                                            </ext:Parameter>
                                                        </Defaults>
                                                        <Items>
                                                            <ext:TextArea ID="TextArea21" runat="server" Width="40" Text="PP" />
                                                            <ext:TextArea ID="TextArea22" runat="server" Width="60" Text="PP" />
                                                            <ext:TextArea ID="TextArea23" runat="server" Width="100" Text="PP" />
                                                            <ext:TextArea ID="TextArea24" runat="server" Width="80" Text="PP" />
                                                            <ext:TextArea ID="TextArea25" runat="server" Width="80" Text="PP" />
                                                            <ext:TextArea ID="TextArea26" runat="server" Width="80" Text="PP" />
                                                            <ext:TextArea ID="TextArea27" runat="server" Width="80" Text="PP" />
                                                        </Items>
                                                    </ext:Container>
                                                    <ext:Container ID="Container12" runat="server" Layout="HBox">
                                                        <Items>
                                                            <ext:TextArea ID="TextArea28" runat="server" Width="540" Height="20" Selectable="False" />
                                                        </Items>
                                                    </ext:Container>
                                                    <ext:Container ID="Container13" runat="server" Layout="HBox">
                                                        <Items>
                                                            <ext:TextArea ID="TextArea29" runat="server" Width="540" Height="20" Selectable="False" />
                                                        </Items>
                                                    </ext:Container>
                                                    <ext:Container ID="Container14" runat="server" Layout="HBox">
                                                        <Items>
                                                            <ext:TextArea ID="TextArea30" runat="server" Width="540" Height="20" Selectable="False" />
                                                        </Items>
                                                    </ext:Container>
                                                </Items>
                                            </ext:FormPanel>
                                            <ext:FormPanel ID="FormPanel4" runat="server" Margins="5 0 0 0" >
                                                <Items>
                                                    <ext:Container ID="Container3" runat="server">
                                                        <Defaults>
                                                            <ext:Parameter Name="ReadOnly" Value="True" Mode="Value">
                                                            </ext:Parameter>
                                                            <ext:Parameter Name="Cls" Value="edi" Mode="Value">
                                                            </ext:Parameter>
                                                            <ext:Parameter Name="Selectable" Value="False" Mode="Value">
                                                            </ext:Parameter>
                                                            <ext:Parameter Name="Height" Value="50" Mode="Value">
                                                            </ext:Parameter>
                                                        </Defaults>
                                                        <Items>
                                                            <ext:TextArea ID="TextArea10" runat="server" Width="40" Text="PP" />
                                                            <ext:TextArea ID="TextArea11" runat="server" Width="60" Text="PP" />
                                                            <ext:TextArea ID="TextArea12" runat="server" Width="100" Text="PP" />
                                                            <ext:TextArea ID="TextArea17" runat="server" Width="80" Text="PP" />
                                                            <ext:TextArea ID="TextArea18" runat="server" Width="80" Text="PP" />
                                                            <ext:TextArea ID="TextArea19" runat="server" Width="80" Text="PP" />
                                                            <ext:TextArea ID="TextArea20" runat="server" Width="80" Text="PP" />
                                                        </Items>
                                                    </ext:Container>
                                                    <ext:Container ID="Container7" runat="server" Layout="HBox">
                                                        <Items>
                                                            <ext:TextArea ID="TextArea14" runat="server" Width="540" Height="20" Selectable="False" />
                                                        </Items>
                                                    </ext:Container>
                                                    <ext:Container ID="Container8" runat="server" Layout="HBox">
                                                        <Items>
                                                            <ext:TextArea ID="TextArea15" runat="server" Width="540" Height="20" Selectable="False" />
                                                        </Items>
                                                    </ext:Container>
                                                    <ext:Container ID="Container9" runat="server" Layout="HBox">
                                                        <Items>
                                                            <ext:TextArea ID="TextArea16" runat="server" Width="540" Height="20" Selectable="False" />
                                                        </Items>
                                                    </ext:Container>
                                                </Items>
                                            </ext:FormPanel>
                                        </Items>
                                    </ext:Container>
                                    <ext:Container ID="Container10" runat="server" Layout="Hbox">
                                        <Items>
                                            <ext:FormPanel ID="FormPanel5" runat="server" Margins="0 0 0 5" AutoHeight="true">
                                                <Items>
                                                </Items>
                                            </ext:FormPanel>
                                        </Items>
                                    </ext:Container>
                                </Items>
                            </ext:Panel>
                        </Items>
                    </ext:Panel>
        </Items>
    </ext:Viewport>
    <br />
    </form>
</body>
</html>