We've all had this warning before, usually right before we crash and burn! In the prop jobs, it means your aircraft is going too fast. Same with the jets.
But when I first started flying flight sim that I would get an overspeed warning during take off and initial ascent. I certainly wasn't going to fast, under 200knts and under 1000ft. So what is that overspeed? The only thing I can think is that it's the overspeed of the turbine.