[Evolution] Problems with gnupg

[suka_at <suka_at yahoo de>]

I have a strange problem with encryption in evolution. I am not able to
encrypt messages to another person, all I get is a warning about "using
secondary key" and later on "no valid adress data, encryption failed". I
don't know what's going on, as encrypting to myself works without a
problem. I am using gnupg 1.06 and evolution 0.15 on Mandrake 8.1. The
strange thing is that encrypting to the same persons key with kmail
works... 

Anyone got a clue what`s happening???

thanks
suka