Edit: Scrub that, the mission works fine on my dad's computer. It's just when I try hosting a LAN game that the error comes up

No idea why though ..?
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I tried creating a simple custom map using the editor [following the handbook].
When I "Validate Mission" in the editor it has no errors. It's saved under:
SilentHunterIII\data\MultiMissions\English\sh3test 1
The game file being called: sh3test1.mis
In SH3 [v 1.4] if I go to multiplayer [LAN], create game I can find the mission. However, as soon as it loads it simply appears with the message "The server has quit. Game over!" I also tried loading it without another player but still got the same message.
I've had a little browse of the forum but couldn't find any answers [sorry if I missed them!].
If anyone knows why it may come up with this message I'd be greatful for the help or if there's anything else you need to know I'll try to let you know what I did =]
Thanks.