The answer to my question was posted by Fred Bloggs on another site (see below). It's correct and it works!
huge thanks to Fred
Hiya,
I hate to say this but you're really going to have to smack it hard on the corners. I've had the odd one like this and I really thought I was going to have to break it off but it gave in and moved.
The only thing I can say is, make sure you've got the 3 (I seem to remember it having 3) screws out of the rear of the lid, then belt it on the front corners.
Dek Messecar, July 2009