Phantom "Stuck Key" Sydrome

A couple days ago, my Mac Pro developed what I'm calling "Phantom Stuck Key Syndrome." The Keyboard Viewer utility shows the "7" key on the number pad is stuck. This is the case whether or not my keyboard is plugged in or even if I plug in my other keyboard.
I am not alone, as this has been discussed at AppleInsider http://forums.appleinsider.com/showthread.php?t=81673 with no solution, so I thought I'd check here.
Any ideas/solutions welcome & appreciated! Thanks!