RequiredFieldValidator Not Working!

ScriptManager
      Multiview
             View 1
             View 2
                 Panel
                     -Contents of Panel are programmatically added
 
Contents of Panel are programmatically added:
For Example I add 3 server controls which are textbox, requiredfieldvalidator, button
I set the ControlToValidate = 'the id of the textbox', EnableClientScript = 'false', ValidationGroup = 'GROUPS' properties of RequiredFieldValidator.
I set the ValidationGroup = 'GROUPS', CausesValidation = 'true' property of TextBox
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