Unexplained CryptographicException : Padding is invalid and cannot be removed

Hi,


I'm getting a bunch of errors in our web application now that state the following:


Error Message:-


Padding is invalid and cannot be removed.

Target Site:-
Int32 DecryptData(Byte[], Int32, Int32, Byte[] ByRef, Int32,
System.Security.Cryptography.PaddingMode, Boolean)

Error Source:-
mscorlib
Error Full:-
mscorlibSystem.Security.Cryptography.CryptographicException: Padding is invalid
and cannot be removed.
at System.Security.Cryptography.RijndaelManagedTransform.DecryptData(Byte[]
inputBuffer, Int32 inputOffset, Int32 inputCount, Byte[]& outputBuffer, Int32
outputOffset, PaddingMode paddingMode, Boolean fLast)
at System.Security.Cryptography.RijndaelManagedTransform.TransformFinalBlock(Byte[]
inputBuffer, Int32 inputOffset, Int32 inputCount)
at System.Security.Cryptography.CryptoStream.FlushFinalBlock()
at System.Web.Configuration.MachineKeySection.EncryptOrDecryptData(Boolean
fEncrypt, Byte[] buf, Byte[ ...