When I try to decrypt package with PGP 6.5.x, I get error: "encrypted session key is bad."

When I try to decrypt package with PGP 6.5.x, I get error: "encrypted session key is bad."

PGP 6.5.x is based on the older OpenPGP specification RFC 2440. To create encrypted package compatible with the older format, in the OpenPGP Task set OldFormat parameter to True.