Don't rail me if this is too simple but.... Did you pull up on the switch to shut off the lockers? The first time I took my 03 Rubi out and used the lockers, I didn't realize that to turn off the lockers, you have to pull up on the switch. I thought I would just keep pressing down on the switch and they would go off but after swallowing my pride and asking my dad, pulled up on the switch and bingo.
The other thing I have heard of is screwing the drain plug in the cover in too deep and that will cause that problem. Maybe the cover got dented so it won't allow release?