CreateProcess fails with error 998 - c++

Question

I have a homebrew Win32 script interpreter called Wintasks which has worked perfectly for 15 years. It dispatches win32 executables using CreateProcess(). It still works fine on Win7-32, but under Win7-64 if any command line arguments are used when Wintasks is invoked the CreateProcess fails with error 998 (memory access violation). Remove the command line arguments from the Wintasks run and all is well.
Wintasks gets its first parameter (the task script to run) from the Winmain lpszCmdLine parameter, and having only that present works. Putting even a blank after the task script filename causes the problem. Parameters can be accessed successfully in all circumstances referencing __argv[].
When run from MSVC5 (as said, it is an old program) under debug everything works, so I cannot solve the problem that way, it is just the Release executable which gives the problem. Running exactly the same copy of Wintasks using exactly the same task script file from a Win32 VM shows no problem.
I would be grateful for any inspiration. I append the code from Wintasks which runs the CreateProcess.
DWORD WinExecX(LPSTR cmdline, int winstate)
{
STARTUPINFO StartupInfo;
PROCESS_INFORMATION ProcessInformation;
BOOL CreateProcessStatus;
DWORD retval;
DWORD fdwCreate = 0; /* flags for CreateProcess */
memset(&StartupInfo,0,sizeof(StartupInfo));
StartupInfo.cb = sizeof(StartupInfo);
StartupInfo.dwFlags=STARTF_USESHOWWINDOW;
StartupInfo.wShowWindow=winstate;
openerr=0;
CreateProcessStatus = CreateProcess( NULL, /*(LPTSTR)name,*/
cmdline,
NULL,
NULL,
FALSE, /* changed 2000-10-18 */
fdwCreate,
NULL, /*envblk,*/
NULL,
&StartupInfo,
&ProcessInformation
);
if(!CreateProcessStatus)
{
openerr=GetLastError();
return 0;
}
elevel=retval = (DWORD)ProcessInformation.hProcess;
CloseHandle(ProcessInformation.hThread);
return retval;
}