Memory issues with CreateProcess - c++

Question

I have written a Windows Service program in C++. One of the tasks it performs is to run a very large business app written in PowerBuilder. It performs a bunch of database processes and transfers data back and forth with SharePoint. The PowerBuilder app gets to a certain point where it aborts and the likely cause is because services have a limited 'desktop heap' compared to normal desktop apps.
As a test we tried using a generic service app called AlwaysUp to run the PowerBuilder app and somehow it has no problems at all. I am stumped as to why AlwaysUp has no issues. Here is the code I use to launch the PowerBuilder app:
// report running status
ServiceStatus.dwCurrentState = SERVICE_RUNNING;
SetServiceStatus(hStatus, &ServiceStatus);
// run the application
event = CreateEvent(0, FALSE, FALSE, 0);
if ( CreateProcess( NULL, CommandLine, NULL, NULL, FALSE,
DETACHED_PROCESS | dwPriority, NULL,
szModule, &si, &pi ) == 0 ) {
// CreateProcess Failed
return 0;
}
// wait for either the process to end or stop event
WaitHandles[0] = pi.hProcess;
WaitHandles[1] = event;
do {
dwError = WaitForMultipleObjects(2, WaitHandles, FALSE, 60000);
switch ( dwError ) {
case WAIT_OBJECT_0:
// process ended
bRunning = FALSE;
break;
case WAIT_OBJECT_0+1:
// event triggered
bRunning = FALSE;
break;
case WAIT_TIMEOUT:
// timeout
break;
default:
// error
bRunning = FALSE;
break;
}
} while ( bRunning );
// close the handles
CloseHandle(pi.hProcess);
CloseHandle(pi.hThread);
CloseHandle(event);