I would assume that most likely you either have sand trapped in between the two halfs or you accidentally twisted the lock too hard.

I've never tried this before, but here's something you might try if you think there's sand inside- Assuming it's an Arriba Hotstick, then the non-yoke end (i.e. the end you hold) should have a rubber grip on it. Remove the grip (actually they usually come off anyway) so that the inside of the stick is exposed. Then take a garden hose and hold it right up to the open end and flush. Perhaps have someone attempt to rotate the stick at the same time.

Otherwise, you might try locking the yoke end to a bench vice and just trying to rotate it that way (perhaps with another person assisting).

sm