I have a claims aware web application using Windows Identity Foundation that has been working well, except on one server. I am seeing the error message shown below in the event log.

Exception information: 
    Exception type: CryptographicException 
    Exception message: Key not valid for use in specified state.

   at System.Security.Cryptography.ProtectedData.Unprotect(Byte[] encryptedData, Byte[] optionalEntropy, DataProtectionScope scope)
   at Microsoft.IdentityModel.Web.ProtectedDataCookieTransform.Decode(Byte[] encoded)

This application is using a very standard implemenation of WIF with ADFS v2. It is not using RsaEncryptionCookieTransform. I am looking for any suggestions on how to diagnose this. Things I have tried so far:

  1. The Application Pool is using the ASP.NET v4.0 identity which has the "Load User Profile" setting set to true.
  2. I deleted the C:\Users\ASP.NET v4.0\AppData folder and saw this was successfully recreated.
  3. I checked permissions on certificate private keys, which were good. I also tried disabling token encryption which did not make any difference.

Any advice would be appreciated.

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