Group Policy - Run Only Allowed Windows Applications

We have a group policy setup to run only allowed Windows applications.  The core processes we allow to run on each PC can be seen below:

acrobat.exe                        Adobe Acrobat Reader 5.0
acroRd32.exe                        Adobe Acrobat Reader 7.0
calc.exe                                        Microsoft Calculator
colleague.exe                         Colleague FrontOffice
collea~2.exe                        Colleague FrontOffice
ctfmon.exe                                        Microsoft Office XP Language Bar
excel.exe                                         Microsoft Excel
gcasserv.exe                         Microsoft Anti-Spyware Server Process
giantantispywaremain.exe                             Microsoft Anti-Spyware
helpctr.exe                         Microsoft Help and Support Center
hh.exe                              Microsoft Windows Help
hkcmd.exe                         Intel Hotkey
iexplore.exe                        Microsoft Internet Explorer
igfxpers.exe                         Intel Common User Interface Module
jucheck.exe                         Sun Java Update Checker Module
jusched.exe                         Sun Java Update Scheduler
kodakimg.exe                         Microsoft Imaging
kodakprv.exe                        Microsoft Imaging Preview
mspaint.exe                         Microsoft Paint
mspview.exe                         Microsoft Picture Viewer
notepad.exe                         Microsoft Notepad
ntspinit.exe                         BCM LANCTE
osa.exe                                         Microsoft Office Startup Assistant
outlook.exe                         Microsoft Outlook
powerpnt.exe                         Microsoft PowerPoint
qttask.exe                                         Apple QuickTime Tray Icon
rcimlby.exe                         Microsoft Remote Assistance
reader_sl.exe                         Adobe Reader Speed Launch
regedit.exe                         Microsoft Regedit
regedt32.exe                         Microsoft Regedit 32
rundll32.exe                         Microsoft Open With Command
shstat.exe                                         McAfee VirusScan Shstat
smax4pnp.exe                         Sound Max MFC Appplication (Audio Card)
square one telephone directory.exe                       Square One Telephone Directory
square~3.exe                         Square One Telephone Directory
tbmon.exe                         Network Associates Error Reporting Service
updaterui.exe                         McAfee Update UI
userinit.exe                         Microsoft Userinit Logon Application
winword.exe                         Microsoft Word
wordpad.exe                         Microsoft Wordpad

The problem we are having is when a user logs onto a Windows XP machine their logon script doesn't run, however when they logon to a Windows 2000 machine it does.  If we turn this policy off and then log the user back onto a Windows XP machine their script will run which leads me to believe we need to add some more processes.  The logon script only maps network drives so we have tried including cmd.exe and net.exe in the above list but with no luck.

We have checked which processes run on the machines during the running of the logon script but cannot see anything we may have missed.  Can anyone tell us what we're missing?

Any help on this would be greatly appreciated.