We have a door that uses a deadbolt lock - one side key and the other side lever. We unlock the door from the inside all the time until one day suddenly the deadbolt wouldn't retract all the way. The lever functions and feels the same as it always has, the bolt just plain won't retract enough for us to open the door.
I disassembled the deadbolt, but of course still could not remove the bolt piece as there is not enough room to maneuver to get it out. We tried using the key from the outside to see if somehow that would work, but the key doesn't even turn now (although there is some question as to whether we have the correct key).
We want to either fix the deadbolt, or in worst-case scenario just get it removed so we can put a new one in.
There does not appear to be an issue with the wood in the door expanding.
Have you tried lubricating it? They sell lock-ease which is a graphite lub for lock assemblies. I use it on my house and vehicle locks and it really makes an improvement on the lock and key movement. If it does'nt work you may have broken something inside.