Validation of viewstate MAC failed

Question

i have these message in only one user of my web ASP.NET application.

Validation of viewstate MAC failed. If this application is hosted by a Web Farm 
or cluster, ensure that <machineKey> configuration specifies the same validationKey & 
validation algorithm. AutoGenerate cannot be used in a cluster.

Any idea how to fix these?

Answer 1

Have you tried specifying a machine key? Even if you're not in a web farm, when the app pool recycles, a new machine key is generated and may be causing your issue.

Answer 2

Here's some information. However, you might want to try installing the .NET 3.5 SP1 before trying anything else, and see if that resolves the issue:

http://blogs.msdn.com/b/tom/archive/2008/03/14/validation-of-viewstate-mac-failed-error.aspx

Answer 3

I also had a single user that was reporting this error message when using my web forms. After some research, I found a suggestion to split the viewstate across multiple hidden fields by using the maxPageStateFieldLength parameter in my web.config. That worked like a charm for my user. Granted, I should still take a look and see why my viewstate is so large, but at least it got him up and running. You can check out the article here:

http://www.andreas-kraus.net/blog/validation-of-viewstate-mac-failed/

Answer 4

it happened to me when I surfed to my web application via ip address. in my case, changing the ip address to localhost fixed it