WebResource.axd throwing exceptions in web farm

Question

We have an array of about 12 servers serving a website. Over the past few hours, one single server has started throwing exceptions for WebResource.axd and ScriptResource.axd

Answer 1

The "?d=yj6PW1hbOvqhMkOh2gYGlw2&t=634207187366247462" is a link somehow (hash or something?) to a resource in the system.web.dll, so understandably with different dll's on that server the link isn't valid.

Answer 2

Found the root cause of the problem. The problem server had a security patch applied which updated System.Web.dll. For some reason our hosting provider didn't update any of the other dll's and in turn this server was generating different encryption keys to the others.

To work out which dll was affected, I used the following to decrypt the webresource.axd query string parameters:

http://blogs.telerik.com/aspnet-ajax/posts/07-03-27/debugging-asp-net-2-0-web-resources-decrypting-the-url-and-getting-the-resource-name.aspx