Some things to try might be to look at the source of the email. Perhaps the Content-Length is incorrect. You could also try using a different module, such as Mail::Sender, Mail::Send, etc. They should all have methods to attach files to the messages, and most of them are pure Perl (ie, they don't call out to sendmail).

If a different module also exhibits the same problem, it might be caused by server problems.

bbfu
Black flowers blossom
Fearless on my breath