MS shared fax (CALL BLACKLISTED)

I have a client running MS small business server 2000. They have been using the MS shared Fax for nearly 12 months now but recently they are experiencing difficulties in sending faxes.

When you examine the OUTBOX in the MS shared fax services console this shows the faxed not send. The status box says “Retries Exceded”.
The extended status box says “Call blacklisted”.

The server faxed using a Intel Ambient chipset modem.

When the fax is going to fail you hear the modem pickup the line but you dont hear it dial it then imediatly gives the status as shown above.

This does not happen to all faxes sent we can fax another office ok, but not the office at where the server is located (yes its not the same line) outgoing faxed go from the server on one number and are sent to a fax machine on another number.

Hope you can help