TLS Connect Failed on Exchange 2003 (SBS 2003)

Hi, was looking for some help in this one!
Some people are reporting that they are not able to send emails to our exchange server. They receive a bounce back “tls connect failed” listing our exchange servers ip address.
We are running Exchange 2003 (SBS Server 2003) with SP2 both on Windows and Exchange.
Any ideas?
Thanks
Matt