I have a customer with an f90bt who complains that the "back" button or any other buuton that appears in the upper right of the screen usually doesn't work without several tries. All other buttons work fine and are in the correct spots relative to the on-screen graphics. Anyone has similar problem or know of a solution? Thanks

Go into > Top Menu > Settings > System Settings > Screen Cal., and calibrate the screen: should do the trick.

Mine has the same prob. After recalibrating, all finger presses work when touching the appropriate button, but the back button seems really fussy about hitting it on just the upper half of the button.