The --decrypt operation should be decrypting the file and verifying the signature. Since the other output is showing that it cannot verify the key used for the signature, I would expect that the verification would fail, which may be the cause of the error code. I believe in older versions we did not include an error code at that particular spot for failed verification. The 3037 line shows that the signature is not verified, but it was not actually showing as an error anywhere.
If you import the public key of the keypair used to sign the files, and use your key to sign that key, it should cause the error message to stop appearing.
Try importing and signing that key (3039:signing key 0xXXXXX), and let me know the results.