I'm using dkim-filter in debian lenny with postfix

Whenever I try to send an email I get the following:

mydomain dk-filter[11513]: 3D65B141974C: bad signature data
mydomain dk-filter[11513]: 3D65B141974C SSL error:04077068:rsa routines:RSA_verify:bad signature

Iḿ sure I'm doing something wrong here but I can't find it. Any ideas?. Thanks for your help.