unusable public key

[Nicolas Rachinsky]

Hallo,

I want  to automatically encrypt and sign a backupfile before it is
transferred to another less trusted machine.

I need an passwordless key for this.

The key is there:
root@pc4 /tmp# gpg --list-secret-keys
/root/.gnupg/secring.gpg
------------------------
sec  1024D/4D347F13 2001-09-13 pc4_backup_sign

root@pc4 /tmp# gpg --list-keys
/root/.gnupg/pubring.gpg
------------------------
pub  1024D/4D347F13 2001-09-13 pc4_backup_sign

Signing works:
root@pc4 /tmp# gpg -v -s tes
gpg: writing to `tes.gpg'
gpg: DSA signature from: 4D347F13 pc4_backup_sign

But I can't encrypt:
root@pc4 /tmp# gpg -v -r 4D347F13 -e tes
gpg: 4D347F13: skipped: unusable public key
gpg: tes: encryption failed: unusable public key


I'm using:
root@pc4 /tmp# gpg --version
gpg (GnuPG) 1.0.6
Copyright (C) 2001 Free Software Foundation, Inc.
This program comes with ABSOLUTELY NO WARRANTY.
This is free software, and you are welcome to redistribute it
under certain conditions. See the file COPYING for details.

Home: ~/.gnupg
Supported algorithms:
Cipher: 3DES, CAST5, BLOWFISH, RIJNDAEL, RIJNDAEL192, RIJNDAEL256,
TWOFISH
Pubkey: RSA, RSA-E, RSA-S, ELG-E, DSA, ELG
Hash: MD5, SHA1, RIPEMD160

under:
FreeBSD 4.3-RELEASE-p20

What is my mistake.

Thanks
Nicolas