If your keyboard is listed on this list of compatible products but it doesn't seem to fit, you may need to lower the tray.

If you look at the tray wings you'll see 2 silver L-shaped brackets that attach them to the desktop. On the wing side there are 4 screws attached. To lower the keyboard remove these screws and attach the bottom two screw holes of the silver bracket to the top 2 holes on the wings. This will give you another inch and a half of clearance.