Fix: Forms authentication failed for the request. Reason: The ticket supplied has expired.

On my windows 2003 server, I've been seeing a lot of information messages like:

Forms authentication failed for the request. Reason: The ticket supplied has expired.

Thrown from ASP.NET 2.0.50727.0

After doing a little search I identified that the issue was caused by not having a fixed validationKey/decryptionKey pair in my machine.config.

Create the key pair by using the code in the Microsoft article below. Insert the key into your machine.config file (which is usually in C:\WINDOWS\Microsoft.NET\Framework\v2.0.50727\CONFIG for .net 2.0). Put the key under the system.web tag.

http://support.microsoft.com/default.aspx?scid=kb;en-us;Q312906