Stuck in the air

I am using a flying script on several of my vehicles and there is an problem. When reaching an altitude of say 160m the vehicle stops going up. At that point it will not go down either. So the up/dn stop working but you can still fly forward/back/left/right ok. This happens at exactly the same altitude every time at a given location. If I move to a different area, the altitude may be 180m when I encounter the problem and will be that every time while at that location.

Has anyone experienced this? Know of a solution??

Thanks

If you have access to it, please post the content of the script so that we can examine it with you? This is an unusual problem, perhaps one that is explicitly included in the script.