Padding is invalid and cannot be removed.

Please tell me why i am getting this error. I am not sure if it is a spider or some other attack attempt.


Error Description: Padding is invalid and cannot be removed.
Error Source: mscorlib
Target site: Int32 DecryptData(Byte[], Int32, Int32, Byte[] ByRef, Int32, System.Security.Cryptography.PaddingMode, Boolean)
Error StackTrace: 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[] modifier, Int32 start, Int32 length, IVType ivType, Boolean useValidationSymAlgo) at System.Web.UI.P ...