ASP.NET: Unable to validate data

Question

What is the cause of this exception in ASP.NET? Obviously it is a viewstate exception, but I can\'t reproduce the error on the page that is throwing the exception (a simple

Answer 1

"a postback is stopped before all the viewstate loads"

I've had this exact problem before, and this was the cause.

Initially we disabled the ViewStateMac property (enableViewStateMac="false" in the page directive) to solve it, but this is not a true solution to the problem and can threaten data integrity. We ultimately resolved it by disabled our submit button until the page had completely loaded, and trimming the size of our viewstate by disabling it on some controls.