I would be surprised if you need to turn the cover Clockwise to unscrew it - are you confident about the information to do so?
Virtually all rotating threads unscrew anticlockwise - unless there's a specific reason to have it the other way - rotating machinery to stop a centre fixing becoming undone for instance - then you will have a reverse thread.
It would be a strange and wicked act by a designer to have a reverse thread on something that did not need it.
If you can grip it try using a damp cloth to give you a better chance.
Good luck...
Peccavi, January 2011
