Mike .. I think I made a post regarding this very issue within the last month :P ... but anyway, the table for all the Roland engravers is a piece of bent metal which under most conditions, doesn't yield a flat, let alone a square to the rails, table. The ONLY solution to this is buying the 'bed leveling kit' from Roland and leveling it. The kit consists of a bunch of strips of material that you adhere to the existing bed and then chucking up the .128" cutter and utilizing the enclosed software that effectively routes the entire surface bed creating a level bed. Typically you take two passes with it.
Good luck!

ps: You could do the same without buying the kit by buying some coran and installing that yourself and engraving that surface level.