Loss of mouse control

I have had this problem a few times now and it's a pain in the ass: if I do something wrong in script (I thinkthis is the cause) I loose mouse functionality ingame (but not in the world editor). But even if I undo my changes, the mouse won't work. I can't figure out why it stops working and the only way right now I can get it to work again is sstart over with a fresh copy of TGE.

Can anyone tell me how to fix it?

Edit: maybe this describes it better: the mouse stays "active" as a mouse cursor, instead of diappearing and thus taking control over the player. It stays in the mode the world editor, gui editor and menu's etc use, control a cursor-image, not the player movement.