If you have screwed up your Entity Data Model, you may be familiar with safe mode when you try to open the model up in the designer.

But the mapping designer has Safe Mode now, too.

Here is what I get when I am in the middle of creating an inheritance in my model which means that some of my mappings are still a big goofy. I tried to get to the mapping details of the derived type and here is what I see:

The error messages for Entity Framework and the designers are really very helpful.