I've had the same problem before, although mine got even worse; sometimes not even registering the click at all, or triple clicking as well as double clicking. I think it even once quadruple clicked. o.O
I never could figure out what the problem was. It wasn't an issue with the settings; none of us messed with the settings. In the end, we had to get another mouse entirely. That's probably what you'll end up having to do.