How can I fix my UPVC french door (bottom locking bar stuck down)?

The main access door of my UPVC french doors locks and opens fine. However, the other door (with the cover strip attached that seals the two doors when closed) is stuck and will not open.
I can turn the key in the lock, move the handle freely etc. and can see the locking bar which protrudes from the top of the door moving up and down freely. The equivalent locking bar at the bottom of the door doesn't move though and is stuck in the frame meaning the door won't open.
Any suggestions for how I could repair this?