Creating levels in the level editor is working. The level that caused the crash was a level that had been working, but stopped working after I had done some modifications to it. I tried to go backwards one step at the time to find out which change caused the freeze, but I haven't succeeded in locating the error this far. I think In the end I found out that I had backtracked myself beyond the last working version without being able to make it work again, so I brought out a backup and continued to work on that. I still have the level that makes the T3 freeze and I hope - eventually - to find the reason for the Fatal Exception.
I have finished the first level in my mission pack and I am now testing it while working on the next level. And now I am getting error messages from the level editor when I try to create a mission pack.

I get a long error message but since it is in Norwegian, I don't know if it will be of any help if I send it to you. Once again I have gone back to the last working backup version, and now it works. I have kept the level that caused the problem and I will try to backtrack myself to find out what causes the error, but I haven't found out yet.
I am sorry I haven't been able to produce any solid feedback for you yet, but I will keep trying.
--SoLan