use Perl

Error during compilation of /path/to/docs/emails/el-GR/some_email.mas: Unrecognized character \xCE at /path/to/docs/emails/el-GR/some_email.mas

how odd..

further investigation leads to this gem :

<% Αν ( !$category->αφορά κάποιο event() ){ %>

which should in fact be :
<% if ( !$category->is_event_based() ){ %>

That's right - somebody translated the perl in my clients email into greek, as well as the content.

Oops