Errors on startup

After I have played with a LUA file, when setting up extra aircraft, I always get an error saying something like '..black\shark\modules\me_aircraft.lua:409: attempt to index local 'unit'.....'

any ideas? even when I set up multi monitor support I get this and then the game wont let me into options or crashes the mission editor.

Im sure im just doing something wrong!

This is something like a standarterror if something with the lua's is wrong.

Just replace the file with the backup you made. If there is no backup just tell me the files you need.

I got the files backed up, I just dont understand whats wrong. My multi monitor setup actually works in game, I just get the error on startup and when I try go into options it just crashes.

And if i edit a file to add an aircraft or edit something I get the same error.. Im using Textpad, could that cause a problem?