VC7.1: MessageBox halts freeze?

[Michael Springer]

I have written a program that talks to a USB device. When
I run the program under WinXP, it works flawlessly. When I
run it under Win98se, it freezes at a particular point
unless I add a MessageBox.

Pseudocode:

Function(){
if(DeviceExists()){
ChangeDeviceMode(); // Restarts device
Sleep(2000);
//MessageBox("This message stops the program from
freezing");
InitDevice();
DoDeviceIO(); // Dies immediately
}
}
I've tried changing the sleep command up to 20 seconds,
and it still fails unless I have the MessageBox. So what
the heck is the MessageBox doing that keeps my program
alive, and is there anyway of simulating this without
using a MessageBox?

---Michael Springer