cant encrypt to Werner Koch's public key!

[Giorgos Pallas]

Hello all!

I must be missing something...
I have downloaded Werner Kochs public key
(http://www.gnupg.org/gnupg-sigkey.html), i have imported it successfully. I
want to send an encrypted file to him (foo.txt).
I give :
gpg -r dd9jn@gnu.org -e foo.txt

and i get :
gpg: No key for user ID
gpg: dd9jn@gnu.org: skipped: public key not found
gpg: opsys.cc: encryption failed: public key not found

--
I give
gpg -r 57548DCD -e foo.txt

where 5754... is the ID of Werner and i get :

gpg: 57548DCD: skipped: unusable pubkey algorithm
gpg: opsys.cc: encryption failed: unusable pubkey algorithm

I have gpg 1.0.4

What am i doing wrong?
Do i need to first sign werners public key before encrypting to it?

thnks
giorgos