Bulk Faxing

I have a Win2003 Standard server. It is also setup as our fax server. We
have a WinXP workstation which faxes through the server. My problem is that
I can send a single fax with no problems but when I try to send bulk faxes
they do not go through. There seems to be no consistancy as to the number of
fax recipients I choose. In other words, I tried sending to 10 recipients
and it worked. Then I tried 20 and it did not. Then I tried 5 and it did not
work again. The fax jobs never make it to the Outbox Fax Queue. The
following event is logged to the event logs:

Event Type: Error
Event Source: Microsoft Fax
Event Category: Outbound
Event ID: 32090
Date: 4/11/2007
Time: 2:28:50 PM
User: N/A
Computer: MARLIN
Description:
The fax was not submitted successfully.

The following error occurred: 4.
This error code indicates the cause of the error.

Sender Machine Name: \\192.168.16.141.
Sender User Name: Administrator.
Sender Name: Administrator.
Number of Recipients: 263.

Any help is appreciated.