PRB: Error message: System.InvalidCastException: Specified Cast is not valid

When you view your ASP.NET page in the browser, you may receive the following error message:

This problem might occur on postback because the control tree hierarchy is re-ordered. On postback, the view state for controls is loaded based on the positions of the controls (indexes) in the control tree. The hierarchy that is created on postback must match the hierarchy that is used initially when the view state is saved.

Make sure that the control tree is re-created on postback in the same order that it was saved at the end of the previous request.

This behavior is by design.