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

I've found the root of this problem in my web site and I finally managed to solve it. This is not a direct answer to your question, but I wanted to share this little piece of information.

In the past I tried everything (including the solution proposed by Jeffaxe, above) but with no result, and I didn't want to set enableViewStateMac="false" (as Raelshark mentions above) to my page, because this just hides the problem.

What caused the problem in my case? The problem was caused by the use of the Intelligencia.UrlRewriter (Version 2.0 RC 1 build 6) module in certain pages of my web site. I was using some SEO friendly links and that was causing the ViewState validation failure. When I used "normal" links (instead of the SEO-friendly links) the problem disappeared!

I reproduced the problem a few times to make sure it was not a false alarm (I use ASP.NET 3.5).

I know that some of you may not use the above module, and still get this error, which implies that the cause is something else. At least, sharing this experience might be helpful to some.