shared printer works for 1 day then stops, but queues print jobs -doesn't print

[win7]

hello,
windows 7 64bit machine sharing a brother laserjet printer.
Installed most current brother print drivers (64bit AND 32bit).
Printing from win7 to printer works great.
Setup shared printer to work from 2 other pcs (winXP pro).
on first day printing works great from winXP pro machines.
By next day, printing from winXP machines doesn't work.
I see the print queue on win7 machine taking the print jobs but it
doesn't print them, they just sit there.
if I reboot machine (win7) it works but by next day the same thing
happens.

What causes this?

thank you