Just had a similar problem on 1997 Escort 1.6 LX 5 Door, where I could lock the doors from inside but they wouldn't unlock. Turned out to be a small coil spring on the driver's door latch assembly. I had to remove the whole latch and security shield to get at it, and found the broken spring laying in the bottom of the door. I reworked the broken end with pliers and refitted it -- Perfect. Thanks to Roco for the tip of looking for the broken spring, which wasn't at all obvious from looking at it.
Dave Hulse
October 2006