Try operating the lock and door handle at the same time, pulling the handle while moving the lock button up and/or down at the same time, etc. For some this has seemed to help, and once the door was open they were able to work on it.
You might also try putting a small tube down to the latch/lock mechanism and put some lube down there, hoping to encourage it to move more freely.
Follow the link in my signature about LEDs in the mirrors for some good images of how to remove the door panel. This could help you if you need to pop it off while the door is still closed. In short, there are 2 plastic rivets on the back edge of the door that you can't access until the door is open. All the rest of the fasteners are accessible while the door is closed.