Error when trying to Decryting Encoded Message

Hi All I encounter below error when BizTalk is trying to decrypt my encoded txt file. Please help is appreciated. Thanks in advanced. Error details: There was a failure executing the receive pipeline: “_ENCODE_RCVPIPE, 2400_01_ENCODE_PJT, Version=1.0.0.0, Culture=neutral, PublicKeyToken=fea1f9f418523c3c” Source: “MIME/SMIME decoder” Receive Port: “ENCODE_RCVPRT” URI: “D:\BizTalk Application\Data\In\encode.txt” Reason: There was an authentication failure. “Failed to decode the S/MIME message. The S/MIME message may not be valid.”.