I had this issue on a Macbook Air that I was playing with today. The Bluetooth mouse had stopped working, and after checking the batteries etc, decided it must be an issue on the Mac itself. I had a look around and tried to find a fix but sadly, just like any old trusty Windows system, a reboot was the simple fix for this problem. Mac users tout about how stable the platform is, but in reality it is just as stable, or unstable as Windows can be. I also have to run updates on the Mac’s around the place just as often as the Windows boxes..