How do I recover an Entity Framework 4 EDMX file when Visual Studio 2010 will not open it?

I have been following the examples from Chapter 2 in an early access edition of Entity Framework 4 in Action whereby one creates a database schema, generates an entity model from the database schema, and then performs some entity customizations with regards to object inheritance, adding complex properties, etc. Everything was great until I closed and then restarted Visual Studio 2010 SP1. After restarting, I can no longer open the EDMX file with t开发者_如何学Pythonhe designer. I get a dialog box stating "Cannot load 'C:\Projects\Test\Test.MyModel\Model.edmx': An item with the same key has already been added.". There is no further information in the Output window.

1. How might one might recover the file?
2. How might one debug the model loading process to find a little more information on what "item" is attempting to load or even what type of "item" it is?

It's an XML file so you can open it up in text mode and see what the problem is. Sounds like there could be items with duplicate names somehow.