And this is my Code I tried..

function prepareAverageWorkExpCombo(emptyValueText) {
var averageWorkExpStore = new Ext.data.SimpleStore( {
fields : [ 'workExp' ],
data : Ext.data.workExp
});
var averageWorkExpCombo = new Ext.form.ComboBox( {
store : averageWorkExpStore,
displayField : 'workExp',
typeAhead : true,
id : 'averageWorkExperiance',
hideLabel : true,
mode : 'local',
triggerAction : 'all',
emptyText : 'Any',
selectOnFocus : true,
resizable : true,
width:100,
listeners : {
'change' : comboBoxListener
}
});

var tt = new Ext.ToolTip({
target: 'track-tip',
title: 'Mouse Track',
width:200,
html: 'This tip will follow the mouse while it is over the element',
trackMouse:true
});
return averageWorkExpCombo;
}

Where am I going wrong. Any small help wil be of great help.
Thanks in Advance