Screwed by Locking HD

[Punky]

Hi everyone.
Thought I'd revist a problem I had several months ago.
Threw in a HD to test things out (just a small 20g).
Worked ok and all (believe it's a WD).
I read some posts about locking the HD and all that stuff.
So I did so. (Using Config Magic)
BAM.
Something happened.
Couldn't boot the Xbox after that at all (flashing Red light). If memory serves I couldn't even boot it from an EVO cd which really blew me away.
Had to put in the original HD again.
I have since shelved that 20g HD, but it's bugging the hell outta me.
Has anyone else seen this? Anyway to fix this?