DJ_Alicorn

From looking at the error, it seems it's having a problem with loading the world. Well mainly the "StevenDimDoors" mod (which is the Dimensional Doors mod). All I could say do it make another world. And you say you have to do this often? Hmm. Well, have you tried restarting your computer? Or perhaps stopping all forms of Java in the Task Manager, then trying to launch the server? I've never actually had this issue, but a few friends of mine have.