Ah well.. that is strange.
I mean, I kind of understand what the errors are saying but I'm not exactly sure why. Essentially you're talking about these two method overloads:
public T Attach<T>(T component) where T : class
return Manager.AddComponent(this, component);
public T Attach<T>(Action<T> configure) where T : class
var component = Attach<T>();
The first error seems to indicate that it's trying to use the second method that takes a configure action but actually it should be using the first.
The next two are also trying to use the second method but this time it's having trouble resolving the type T automatically.
The last error.. wait a second..
I think you might have a version mismatch going on? Are you referencing the 1.1 NuGet packages? The code you've posted is probably from the 2.0 demos.
Btw.. lots of things are changing in the
develop branch right now making way for 2.0. The ECS in particular is getting a complete overhaul so anything you do now will definitely break.