it seems we found an issue using the lastest version in a non "en-Us" environnement : when used to call a method with a Date parameter, Ext.Direct.Mvc return an invalid date or an exception when parsing the String : this problem occurs with the basic sample included with the source.
After looking at the source code, it seems the issue occurs in ReadJson method of the RequestDataConverter class where each JValue sent from the client are converted to string : if the JValue contains a DateTime the toString must specify the InvariantCulture to avoid parsing issue in the DirectValueProvider. To resolve the problem we've only add a check if the value is an IFormattable. Hence the following modification in the ReadJson method resolves the problem :
if (value is IFormattable)
data.Add(value == null ? null : ((IFormattable)value).ToString(null,CultureInfo.InvariantCulture));
data.Add(value == null ? null : value.ToString());