SBS 2008 / XP Fax clients

I have an SBS 2008 server handling my faxes with 32 bit XP and Vista clients. My Vista clients work great, but my XP clients cannot connect properly. When I install the fax on an XP client it looks fine, but if I open it to view faxes, I get the message, "All fax printers are inaccessible." If I try to send a fax I get the message, "The server information cannot be retrieved. The fax wizard will close now." I've tried all the steps listed here: http://social.technet.microsoft.com/Forums/en-US/winserverprint/thread/f10cd018-abb7-4fc6-9111-2b4203184a1c?prof=required but with no success. What else is required?

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Daryl Sensenig