I have had endless issues with stored procedures and EDMX. I created a procedure, updated the model from the database, and all worked. I then removed a column and added a ne
(This solution is for EF 6. I have not tried in other EF versions. It works nice.)
Go to Model browser. MyStoreProc is the name of the stored procedure (as an example). MyStoreProc will appear in 3 places.
Delete all three from model. Save the edmx (by clicking in the window then ctrl+S). Then right click and click update the model from database. Then add the updated stored procedure and Save again.
Solved without any hassle :)