It's hard to know what's happening without more information. I would suggest the best thing to do is to create a basic new mission, add the modules one at a time, test the results of adding each in the editor, then actually save the mission and load it normally. I realise this is a bit tedious to do, but you'll soon isolate which module is causing the errors to appear.
Some people have problems with certain modules (I'm one of them) and it's proved very tricky to track down exactly what is causing that. I'm hoping you're not one of these affected people and that it's something more generic that's happening. The module which has caused the most problems is the Ravage settings module.
I would also suggest that as you add each module, you save your mission under a different name so you can always go back to a working version if you hit a problem. Removing the troublesome module or setting does not always clear the error.