App only runs in Safe Mode of Windows XP

[Dude]

A user of one of my apps (Win XP, 32bit) says that my app only runs when his PC is booted in Safe Mode. That is, the app's main loop (which reacts to systray events, etc) apparently doesn't respond in normal mode. He says clicking the systray icon and using the app's hotkey doesn't do anything, but in Safe Mode, it all runs fine and the main loop responds normally.

How do I even begin to troubleshoot this issue? I have no idea what could be wrong. Also, he's not the first to report it; I've been told it by about 3 other XP users, but this guy is the first to test it in Safe Mode, which works for him. He said he's disabled his anti-virus and anything that could potentially interfere with my app, but they shouldn't be a concern anyway.

Thanks in advance for any generic advice.

[TI-994A]

...app only runs when his PC is booted in Safe Mode.

The blocked processes in question could rule out any UAC issues. Offhand, it sounds like a Windows security issue. Some installed security software might be flagging the app and blocking those system processes.

High probability, as PureBasic apps have been victim to false-positives before.

[Lunasole]

Thanks in advance for any generic advice.

The most generic is logging, just dump to a log file results of any key functions your app uses on initiation (i.e. CreateWindow and so on), then it should get clear which step fails.