Note: This known issue was fixed in 6.2 rev. 101105 (Update-5), 6.3 rev. 101022 (Update-3), and 6.4 rev. 101124 (Update-1).
Reference number: 334587
Date published: October 01, 2010
After installing an update from Microsoft that addresses the ASP.NET security issue described in Microsoft Security Advisory (2416728), Sitecore CMS may be throwing unhandled “HttpException: Unable to validate data” errors when previously authenticated users are trying to access the application.
This is caused by Sitecore CMS trying to authenticate a user using the ASP.NET authentication cookies that may still be contained in the web browser, but are no longer considered valid by ASP.NET.
- Copy the Sitecore.Support.334587.dll file to the "/bin" folder of your solution.
- In the web.config file, replace the line
<add name="forms" type="Sitecore.Security.Authentication.FormsAuthenticationProvider, Sitecore.Kernel" />with
<add name="forms" type="Sitecore.Support.Security.Authentication.FormsAuthenticationProvider, Sitecore.Support.334587"/>