Driver change to 5440 Deskjet causes it to disappear from configuration

I have several PC's running XP (Home & Media Center) in a workgroup,
which communicate with our main computer through the Remote Desktop.
We've had trouble getting the local printers to "Show up" on the host
side, and have had to reconfigure the HP 5440's to be 990c's (HP told
me this was a "Universal" driver). I have had this work every time
until today.

On a new PC (running XP media center) it allows me to change the driver
to 990c, but once I do that, it removes it from the "Printers and
Faxes" configuration. I even tried changing it to an LPT port, to no
avail.

Any idea why this method would suddenly no longer work? It is possible
there is something different about this PC from the others, but can't
imagine what.

Thanks for any help.