This implementation is not part of the Windows Platform FIPS validated cryptographic algorithms‏

After you upgrade from Microsoft ASP.NET 1.1 to Microsoft ASP.NET 2.0, some ASP.NET-based applications may not function correctly. Additionally, when you access ASP.NET Web pages that have ViewState enabled, you may receive the following error message:
[InvalidOperationException: This implementation is not part of the Windows Platform FIPS validated cryptographic algorithms.]

This problem occurs when the following conditions are true:
-The HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Lsa\fipsalgorithmpolicy registry subkey is set to 1.
-ASP.NET 2.0 uses the RijndaelManaged implementation of the AES algorithm when it processes view state data. The ReindaelManaged implementation has not been certified by the National Institute of Standards and Technology (NIST) as compliant with the Federal Information Processing Standard (FIPS). Therefore, the AES algorithm is not part of the Windows Platform FIPS validated cryptographic algorithms.
Resolution:-
http://support.microsoft.com/kb/911722

Note:-Please follow each step carefully within this document and the issue will be definately resolved.

I hope the above document helps you to overcome the above mentioned error message. Thanks!