Need help with cybercash decryption errors

Hi I am having a problem with my cybercash routines. I am using cyberclass and I get the reply from cybercash as follows: mac = 3>JÄ `çe„æ??ú$:ç1$ message = Ù¶v’½ÏÆØíñª™<?.æ¬a²çZÛ= =J–: ±/Kõ݈V*¯ÖCÕËÉ;Knò¼ÇÒ?<³y•<(JáòkˆÕ\ú9úp“¹Sˆþè*¦ ÏÇ session-key = Fri Dec 8 18:15:26 EST 2000 #27203 MStatus = failure-hard MErrMsg = Response non-decodable. MErrCode = 4 What causes decryption errors like these? I have checked my merchant_conf file and the Merchant Key is correct, any ideas as to where to look for problems. Thanks Nick Steele