Fax service loses fax modem after successful use

WinXP box, broadband Internet connection, SmartLink PCI bus
FAX modem for those few occasions when I need to send or
receive a real old fashioned fax. If I bring up the Fax
Console and choose "Receive a Fax now...", 90% of the time
I get "There are no fax devices. Please install a modem
that supports fax operations." Or if I generate a fax
throuh the fax printer, it gets queued and a system event
gets logged: "Fax Service failed to initialize any assigned
fax devices (virtual or TAPI). No faxes can be sent or
received until a fax device is installed."

Restarting WinXP allows all fax operations to proceed,
including queued outbound faxes. Therafter things will work
for a while, but by the next day fax operations are
unlikely to be working.

I've scanned the event logs, and I cannot see any event
which corresponds to the point at which the modem driver
and FAX subsystem become unglued. All of the drivers are up
to date.

Any ideas?