Internal Server Error

[MagicMover]

Please help! I'm a new WP user and I installed Quick Cache, activated and got this message:

You do not have sufficient permissions to access this page.
Internal Server Error

The server encountered an internal error or misconfiguration and was unable to complete your request.

Please contact the server administrator, cgiadmin@yourhostingaccount.com and inform them of the time the error occurred, and anything you might have done that may have caused the error.

More information about this error may be available in the server error log.

WHAT DO I DO NEXT? I've deactivated, deleted and re-installed but still get the same error message.