Okay been looking into it, and there is a few other people who have had the same issues as us. It seems that the 1.8 update tries to alter the maps and as a result fucks up and dies.
Soooooooo the bad news, I've had to make a new map
The good news is its working fine with no lag.
Bad news you have to build new houses
Good news the 1.8 update added some cool caverns to find and some prebuilt houses etc to find.
So its up and running now.
Any lag issues or other issues let me know.