An event is trying to walk around on a map which isn't directly connected to the map the player is currently on. The code that's causing the problem only checks the current map and directly connected maps to see whether the event is moving onto a valid tile; it doesn't check connected-but-one maps and so forth.
Have a look at your map connections. Open them in the Visual Editor and save them again to make sure. There needs to be a connection between a map and any "nearby" map (both directly connected ones and ones within about 5 tiles of it in any direction).
This is probably why remaking the map from scratch tends to work - the user would tend to recreate the map connections as well, which are the problem.
Thanks Maruno. I deleted everything in the connections.txt and redid them and as far as I can tell that fixed it. :D
I while we are talking I have another question and don't want to start a new discussion on it. How do I change the text colors in the text entry screen? I want all letters on the screen to be white and can't figure out how.