Strange problem with Verisign

I've signed up to Verisign (been using them for a couple of years)

Never noticed before, but if I send email from Outlook 2000 and I attach a
file, but NO subject and NO body text. The email arrives with a certificate
error saying it has changed.

If I add a subject, and/or any body text, it works fine.

thanks

Clive

Clive