The following is a solution given:
Here are the steps you need to take to fix the issue:
1. Go here: http://www.developmentnow.com/articles/machinekey_generator.aspx and click on "Generate Random Keys!" button. This will generate some code. Copy the code from ASP.NET 2.0 textarea.
Here is what you need to do on *every* machine in your web farm:
2. Locate Machine.config file.
3. Locate the <system.web> section in this file.
4. Replace the <machineKey> section with the output generated in step 1.
5. Save the configuration file.
6. Restart IIS.
This will ensure that the same key is used to encrypt and decrypt some data in webresource.axd on all machines.