Some XP workstations do not get there IPrint driver profile installed.Im
running IPrint clients 4.16 with firewall disabled.

This comes from the ippErrs.txt if it helps.

Module: iprntctl.exe
Trace Info: registry.c, line 5191, thread 00000190
Routine: TrayIconGetAndDeleteMessage - RegOpenKeyEx failed 2
Error: The system cannot find the file specified.

Ive also install the two XP patches from MS