PGP does not accept session key

[Stefan Nobis]

I have a problem, sending encrypted mails to a PGP user. All mails i
send can't be decryptet by PGP (V 6.0.2). It bails an error message,
which says that the session key is bad. I used GPG 0.9.5 on Linux
2.2.9.

I found a statement in the docs, but i don't understand it:

     * PGP 5.0 rejects an encrypted session key if the keylength
       differs from the S2K symmetric algorithm. This is a bug in its
       validation function.

What does this mean?

-- 
Until the next mail...,
Stefan.