“Why can’t I trigger a manual blue screen crash by injecting the magic key sequence?”

A customer was developing an automated test that required the system to suffer a blue screen crash. They configured their test systems to crash when the ScrollLock key is pressed twice while holding the Ctrl key, and they wrote a simple program that ran as administrator and injected the appropriate keystrokes. But no crash occurred. What did they do wrong?
↫ Raymond Chen

Does anyone here not love a Raymond Chen mystery?