To improve an older project I am forced by the circumstances to use VS 2008 and Framework 3.5 - I have issues with the edmx showing bizarre behavior and not updating the entities as required.
The edmx throws me the above error, but when I go to the respective table and right click it - "Update Model from Database" there is no change, the error is still there.
If I delete the table from the diagram by selecting it and pressing del, then in the Model Browser It disappears from the .Database but when clicking "Update model from Database" I can't see i in the "Add" list, all I can do is "Refresh" the table since I still see it in the refresh list (which should not happen because I deleted it! )
Check the xml file of your model, it's probably still in there somewhere. Try deleting it manually from that XML file, then try to update again. Be sure to take backups though.