This happens when I'm lagging. Eventually (30sec to 5min later) I get the rubberband from hell replaying everything that happened at 100x speed. Then I can use them again. Oddly I can launch torpedos during this time, they just don't do anything. No Phasers, can't change speed, can only turn at approx the rate you can when stopped dead.
This also happened when my shift key stuck for some reason... I guess I should quit spilling coffee on my keyboard.