I'm not insane right? This code could not possibly cause this problem could it? As you can see it sets up a non Windows piece of software and MSN Messenger and I'm getting the problem! Windows Registry Editor Version 5.00 [HKEY_CURRENT_USER\Software\Pathfinder] "AutoClose"=dword:00000000 "ExcludeBots"=dword:00000001 "IncludeEmptyServers"=dword:00000000 "Speed"=dword:00000004 [HKEY_CURRENT_USER\Software\Microsoft\MSNMessenger] "AppSettings"=hex:02,02,01,00 "DisableTabs"=hex:01,00,00,00 "InstalledMSNCertificate"=dword:00000000 "RTCTuned"=dword:00000001 "ShowCustomEmoticons"=hex:01,00,00,00 "TaskListState"=hex:03,00,00,00 "AlwaysOnTop"=hex:00,00,00,00 "CrossPromoRefreshLogon"=hex:01,00,00,00 "DSBkgndMode"=hex:01,00,00,00 "MobileFilter"=hex:01,00,00,00 "SharePassportCredentials"=hex:00,00,00,00 "ShowCustomEmoticons"=hex:01,00,00,00 "ShowEmoticons"=hex:01,00,00,00 It seems that the second I modify the HKCU stuff at T-13 it breaks something! I've had HKLM stuff going in before but added that in post-install and it failed then so I instantly got rid of that as a potential problem. I am totally lost now!