I have solved the problem. It is because you've upgraded to EF 6.X from EF 5.X your edmx is still on the old legacy generation strategy.
What you need:
Update all projects using Nuget to EF 6 release
For C# download http://visualstudiogallery.msdn.microsoft.com/66612113-549c-4a9e-a14a-f629ceb3f89a
For VB.net download http://visualstudiogallery.msdn.microsoft.com/ff479d55-2c85-43c5-a4d6-21cd659435ea
After installing 1 of these extensions you want to backup your edmx and designer files (or use source control). Restart Visual Studio.
After restarting Visual Studio you want to go into your project and:
- Get into the diagram design surface
- Right click and select "add code generation item"
- Select the "EF 6.X Entity Object Generator" and call it something appropriate like "Template.tt"
- Let the generation occur
- Go back to the design surface and ensure that the Code Generation Strategy is now
T4
- Delete the designer file created by the older legacy EF 5.X
This gives you your ObjectContext
derived context as well as everything matching the newer EF 6.0 namespaces.