Muzza,
I had somewhat of a similar problem when using Darrel's Instant Interrupts.
When I copied/pasted his posted code over my typed "problem" code of the exact wording, it worked!

I thought he had some type of special code in his typed code. But it turned out that I had the Reserved Word Formatting set to "Uppercase all" so I fooled myself into thinking I typed a certain word uppercase when it wasn't.
I immediately changed it to "Default" so I would see what I'm actually hen pecking!

The MSCP setting is under: View --> Editor Options --> Highlighter, then Reserved Word Formatting at the bottom.

You have yours set to "Lowercase all" which may be hiding the real typed word causing the headache!