WebResource.axd - Invalid ViewState

I keep seeing these errors in our error log. Any ideas how i can figure out where its coming from, or better yet how to fix the problem?

System.Web.HttpException: Invalid viewstate. at System.Web.UI.Page.DecryptString(String s) at System.Web.Handlers.AssemblyResourceLoader.System.Web.IHttpHandler.ProcessRequest(HttpContext context) at System.Web.HttpApplication.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)

Update Here is what I have tried so far - we are running a single web server (no farm)

• Adding a Machine Key value to web.config

MS has an open bug report as of 6/14/09 reguarding this issue:

https://connect.microsoft.com/VisualStudio/feedback/ViewFeedback.aspx?FeedbackID=434997&wa=wsignin1.0