Error message when replying to email

[Jmorris]

I connect remotely via dial-up VPN connection and able to
receive emails, so the server connection is OK. I was
able to send emails to both an inside and outside email,
however when I reply to certain emails, I receive an
error message "Network Problems are preventing connection
to the microsoft exchange server".
I am running W2k and Outlook 2000 and the server is
Exchange 5.5.

Any help would be appreciated.