Left shift key inserts ± (plus/minus symbol)

When I try to use the left shift key and hold it down for more than a half-second or so it will insert the ± symbol. Not being the speediest of typists, this has rendered the key useless (besides being a shortcut for that symbol, of course). This occurs in all profiles.

I am using a Macally ICEKey keyboard with the latest drivers. The behavior occurs when I set the keyboard to the "unknown generic keyboard" option, as well. I tried uninstalling the drivers and trashing the com.apple.keyboardtype.plist file, but the problem continued to occur after it went through the generic keyboard setup on reboot. I should also mention that the keyboard worked fine for a few months before this problem arose.

The only other USB keyboard I have is a generic Dell keyboard (that does work with a Windows box), but when I plugged it in after removing the Macally it was not recognized by my Mac, even after reboot.

Besides trying another keyboard that is confirmed to work with Snow Leopard, are there any settings I should change (the language and character settings are default English with an ANSI keyboard layout) or other diagnostics I could try?

Thanks,

Sam