To add to Ed's reply, I've also had success fixing the problem by pressing Alt+Tab.

>Some times in my application, the Tab key acts like Alt-Tab.. i.e. switches between active windows not between fields.
>
>Any ideas what causes this and how to fix it?
>
>The only fix I know is to shutdown completely and reboot the machine. Needless to say this is a major pain in the neck.
>
>TIA,
>Mike