I know this thread is three years old, but I had the same problem recently. The metal plate is rivetet with plastic rivets over the actual keyboard. I just scraped the heads of the rivets with screw driver and after this the plate can be removed. This is caused no problems, if you afterwards screw all parts together again the keyboard and the plate are fixed even without the rivets. (you could maybe use glue for fixating, but this isn't necessary.