Was playing with the N7 Destroyer at London on Silver. Suddenly (I think it may have been an ammo crate), I have no more a counter for grenades and couldn't shoot my weapon (Harrier) anymore. Also, I had no grenades and couldn't pick up new ones, so couldn't use those either. I then switched to the Missle Launcher, but I couldn't fire it either nor could I switch back to my Harrier.
Below, you see an screenshot of the situation. Notice the accuracy of Harrier while not in cover!