getting error Invalid postback or callback argument. when on postback

Hello All,
i have used modalpopup control and radiobuttonlist contains on it.now i want to call radiobutton selectedindexchange
but i m getting an error when i do click on changeevent
Error : Invalid postback or callback argument.  Event validation is enabled using <pages enableEventValidation="true"/> in configuration or <%@ Page EnableEventValidation="true" %> in a page.  For security purposes, this feature verifies that arguments to postback or callback events originate from the server control that originally rendered them.  If the data is valid and expected, use the ClientScriptManager.RegisterForEventValidation method in order to register the postback or callback data for validation
if any one have any idea about this let me know as earlier as possible.
Thanks In Advance.
any help will be appriciated.
Thanks,
Khushboo Nayak.