Forms Data Controls :: PageRequestManagerServerErrorException In Gridview?

Iam using v2 2008.I have 2 gridviews in update panel and one updateProgress control above updatepanel.First grid contains users and second grid contains module names and 2 checkbox columns ,also i have a submit button.

I will select users in first grid that select one ow at time then accordingly second grid will be displayed with permissions ticked in checkboxes,i can also deselect them and save into database

My issue here when am selecting users in first grid and permissions are checked in second grid and i deselect or select according to my requirement.When am doing this process for different users in the grid for 2 -3 times it works good but for the 5 th time get this exception

Microsoft JScript runtime error: Sys.WebForms.PageRequestManagerServerErrorException: 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

My code

.cs file

protected void gvAssociatedUsers_RowDataBound(object sender, GridViewRowEventArgs e)
{
if (e.Row.RowType.Equals(DataControlRowType.DataRow) || e.Row.RowType.Equals(DataControlRowType.Header))[code]....

so i have registered callback or post back data for validation even then am getting this exception.do u want any other code related to grid as i have posted only some of the code which relates exception