What else can cause 'Padding is invalid and cannot be removed" exception with WebResource.axd?

Recently, a couple of my applications have started throwing exceptions with the message Padding is invalid and cannot be removed intermitently

My applications already have a machineKey specified in the web.config as sug开发者_如何学Cgested in this thread

The applications are deployed to a single Windows 2003 server running IIS6.

Usually on webResource.axd this is happens because the key that follows the webResource.axd on the url, have been convert to lowercase from the crawler, or in general changed