Hi aclements,
Do you have a file that was encrypted with a key pair elsewhere? IF the file was signed, you should have been provided a public key from the trading partner that sent you the file and imported it to your key ring.
The most likely causes are either the public key you received from your trading partner was not the one used to sign the file, your public key was not used to encrypt the file, or you are pointing to a key ring that does not contain the correct public key received along with your private key for decrypting.
From Forum Post:
post1364.html?hilit=matching&sid=36405157e3740d04d6b93546a6bb6d60#p1364
