"Signature of the body and declaration in a method implementation do not match"

Question

UPDATE: I think I've eliminated Unity from the equation. See below for more details.

UPDATE 2: I think I may have eliminated Entity Framework fro the equation. See below for more details.

I have some code that is building a unity container, but it started failing with the above error message out of the blue. It works on other people's machines, but not mine. I deleted the folder the solution was in and refreshed everything from source control to ensure I had nothing that could be causing issues (e.g. duplicate assemblies lying around from a previous build).

Here is part of my code:

public static class UnityBootstrapper
{
    public static IUnityContainer Initialise()
    {
        Trace.WriteLine("UnityBootstrapper.Initialise()");
        var container = BuildUnityContainer();

        DependencyResolver.SetResolver(new UnityDependencyResolver(container));
        return container;
    }

    private static IUnityContainer BuildUnityContainer()
    {
        Trace.WriteLine("UnityBootstrapper.BuildUnityContainer()");
        var container = new UnityContainer();

        // Other dependencies are registered here

        // If the following line is commented out the container is build
        // but, obviously, it won't resolve this dependency.
        container.RegisterType<IUserAccessEntities, UserAccessEntities>(WebRequestLifetime);

        // Other dependencies are registered here

        return container;
    }

The code apparently fails on the call to BuildUnityContainer(), and I can see that the trace statement I put inside that method is never displayed.

However, if I comment out the line that registers the UserAccessEntities class (which was code generated from Entity Framework 5) then the container is built. Naturally, when I ask for that dependency it can't resolve it, so the code just fails elsewhere.

I've Googled for solutions and they all seem to resolve around generics and moving the generic type from the method to the class level. I can't do that as EF5 creates the class and it puts generics on the properties. e.g

 DbSet<MyTable> Tables { get; set; }

The only other thing I can think of is that I've extracted an interface from the EF5 generated class called IUserAccessEntities and the problem could lie there... but I used ReSharper to generate that, so it should be perfectly aligned.

UPDATE

Just to eliminate Unity from the equation, I tried to new up the UserAccessEntities on its own

    private static void TestUae()
    {
        var uae = new UserAccessEntities(); //container.Resolve<IUserAccessEntities>();
        Trace.WriteLine("Got the entities: " + uae);
    }

And the call to TestUae() fails instead.

UPDATE 2

I created a new class, AlternativeEntities based on the interface I'd previously extracted. When I try to construct that directly it has a new exception: Method 'Set' in type 'AlternativeEntities' from assembly 'UserAccess.Model, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null' does not have an implementation.

However, it does. There are two methods called set, both of which I've given a basic implementation:

public class AlternativeEntities : IUserAccessEntities
{
    public DbSet<TEntity> Set<TEntity>() where TEntity : class
    {
        Trace.WriteLine("public DbSet<TEntity> Set<TEntity>() where TEntity : class");
        return null;
    }

    public DbSet Set(Type entityType)
    {
        Trace.WriteLine("public DbSet Set(Type entityType)");
        return null;
    }
// Other methods and properties here.
}