ASP.NET Error:The state information is invalid for this page and might be corrupted

I had searched many pages and finally this is working for me

protected override object LoadPageStateFromPersistenceMedium() 
{ 
return Session["_ViewState"]; 
}
protected override void SavePageStateToPersistenceMedium(object viewState) 
{ 
Session["_ViewState"] = viewState; 
}