I had this happen with one of the original Aladin Tecs. I guessed it was related to salt crystals. The warm freshwater didn't work for me either. I ended up getting an o-ring pick and prising it out.
You may want to get in touch with the LDS or Scubapro direct to see if they can rectify the problem or replace the unit (as it appears to be a common problem).
Cheers,
Nick