Connection error: your terrain file doesn't match the version th

hey guys, can someone please help me with this problem? i am just starting the multiplayer part of my game, but when i try to run a multiplayer game and try to join i get this error msg... "your terrain file doesn't match the version that is running on the server", both code is identical running on seperate computers on a LAN, thanks!

Edit:
This and other wierd errors and crashes were side stepped by changing from 1.1.1 to 1.1.2, now you know : )