Weird, when I right-click a key mapping to remove it, it actually removes the text, it doesn't say 'Clear' Also, do you have a joystick or gamepad plugged in? If so, make sure that all of their axis are centered, that includes the common 'throttle' axis. If that axis is either fully up or down, it will confuse most 'key mapping' systems in any programs. However, in these cases it usually says something like Axis4+ or something like that. If it really says 'Clear' ... hmmm... I dunno, do you have some special keyboard with function keys? There might be some kind of toggle key called 'Clear' that is on, or something.