there was an error running the selected code generator unable to retrieve metadata for
PROBLEM:
I have updated to Visual Studio 2013 update 2 and now I cannot scaffold controllers.
The problem is not project specific: when I try to scaffold a controller, I get the following error in ALL and ANY project:

There was an error running the selected code generator:
'Exception has been thrown by the target of an invocation.'

It was working before updating to Visual Studio 2013 update 2.
A combination of things have worked for me:

Upgrade to Visual Studio 2013 Update 3. Upgrade Entity Framework to 6.1.1Modify the context configuration to use IDbSet<…> instead of DbSet<…> (I have heard that this can affect using async actions, but not apparently in my case, as I use this in my login actions, etc, as supplied by ASP. NET Identity 2 sample Nuget package).

Quite why this combination works, I have no idea. But then given the thundering silence from MS, I am probably not alone. I guess update 2 just didn’t work…