Treo 750 cannot Send email to internal excahange users

I have a Treo 750 that uses Active sync to connect to my Exchange server.
Everything works great except when I try to send email to my internal
exchange users. When I create a email and send to an internal email account
from my global list they do not recieve the email. However it shows up as
being sent in my sent items box both on the treo and in Outlook 2003. But the
intended user never recieves the email or do I get any error messages. I can
send email to people outside the organization with no problems.

Strangely If I create a new email on the Treo with a bogus email address and
also choose an internal contact it will send to the internal user. Other
notes I am using Exchange server 2003 sp2, Windows 2003 sp1 and have others
in my organization with Treo 650's and Trea 680's that have no issues.
Appericate any assistance anyone could provide.