If, in your call to CreateProcess, you put the module name as lpApplicationName and do not repeat it at the beginning of lpCommandLine then the Image File Execution Options registry key will not work: The system will launch the debugger with lpCommandLine only and it won't have a module name to launch. E.g., lpApplicationName="notepad.exe" and lpCommandLine="foobar" and a "notepad.exe" key under "Image File Execution Options" with string debugger=vsjitdebugger.exe will attempt to launch "vsjitdebugger.exe foobar", not "vsjitdebugger.exe notepad.exe foobar". (Observed on Windows XP Pro SP3.)