If I use my number pad, my mouse stops working!

Ok- so a bit of an odd one;
For the last two weeks, if I type any of the keys on the number pad of my keyboard, my mouse button suddenly doesn't work. The mouse moves around but the click doesn't do anything. I've tried different keyboards and mice and nothing works! The only thing I can then do is reboot via Terminal and then it's ok again... until the next time I hit any keys on the number pad (which I need to use all the time).
Specs below- anyone encountered this before?
Thanks

OSX v10.6.7
Model Name: Mac Pro
Model Identifier: MacPro1,1
Processor Name: Dual-Core Intel Xeon
Processor Speed: 2.66 GHz
Number Of Processors: 2
Total Number Of Cores: 4
L2 Cache (per processor): 4 MB
Memory: 7 GB
Bus Speed: 1.33 GHz

I recently started having this same issue. I am using a bluetooth wireless mouse and if I start using the numpad on my iMac's keyboard I can no longer click with it.

EDIT: Found the solution upon another forum. Seems I had turned "mouse keys" on some how.