I have had a few reports about the sultan’s area of late…I will have to check it out. The auto-start event that jails you is failing to start, which needs to happen for Ch.4 to end.

http://www.rpgmaker.net/games/82/downloads/1232/

Download the new map file and paste it into your game directory (overwriting the existing one). Then (hopefully) everything should work. Or at least allow you to proceed through the game.