OT - Winxp Dialup Dramas

Heres one for the XP Xperts out there.

I have a friends PC here that throws a Error 633 every time you try to 
use the dialup modem.

I have removed and reinstalled the modem ( both physically and software )
I have recreated the dialup connection numerous times.
The error occurs on any and all COM ports assigned to the modem.

I have replaced the modem with a known good unit and repeated all of the 
above steps.

There is no other fax/phone software running ( that I am aware of ) and 
yet we still get the 633 error ( busy COM PORTS ) as soon as the dial 
button is clicked.

The error is instantaneous - never gets as far as looking for a dial tone.

any ideas?

cheers
Chris