Bad Data error

 Hi.  Users sometimes receive a Bad Data error on my website.  There seems to be no pattern to when it happens, tends to be every few weeks.  Any ideas on the cause?  Last time a user got it they just clicked back and did what they were doing again and it worked fine. I've looked online, but can't seem to see anything that will help.  Maybe the page isn't loading completely when the users click a button?

Error Message: Bad Data.

Trace: at
System.Security.Cryptography.CryptographicException.ThrowCryptogaphicException(Int32
hr) at System.Security.Cryptography.Utils._DecryptData(SafeKeyHandle hKey,
Byte[] data, Int32 ib, Int32 cb, Byte[]& outputBuffer, Int32 outputOffset,
PaddingMode PaddingMode, Boolean fDone) at
System.Security.Cryptography.CryptoAPITransform.TransformFinalBlock(Byte[]
inputBuffer, Int32 inputOffset, Int32 inputCount) at
System.Security.Cryptography.CryptoStream.FlushFin ...