That's right, Defensio plugin was developed against the latest svn and
provides plugin translations that are currently only in svn. If you
remove line 83 which looks like:
$this->load_text_domain( 'defensio' );
Then it should work on 0.4.1. However you won't have the "training"
feature of Defensio as it too requires a hook only available on svn,
but it will still filter your comments and put the spam in your spam
bin; it just won't report any "false positives/negatives" to Defensio
to "train" it.
Let me know if you have any other probs.
Thanks,
Matt