Testing on Win7 (64bit) with Firefox11 and IE9, I got the following when rapidly and repeatedly pressing the up arrow (IE just hangs, but Firefox gives the error message):
"Warning: Unresponsive Script
A script on this page may be busy, or it may have stopped responding. You can stop the script now, or you can continue to see if the script will complete.
Each error response gives a different line number.
The .capx is here:
Not sure if my events are configured in a way that causes the error (I'm wondering if it's the OR block), but I figured I'd post it.