I'm getting a bunch of errors when I upgraded Unity to 5.1

[pangyan]

I just upgraded to 5.1 for Unity. I now get a bunch of errors when compiling the 2D toolkit. Errors like this:
Error   253   The type or namespace name 'tk2dUIManager' could not be found (are you missing a using directive or an assembly reference?)

There are well over 350 errors so it looks like most of the classes are just not being compiled.

In particular an error like this caught my eye in this line:
allTransforms = (from t in allTransforms where t != batcher.transform select t).ToArray();

The error is:
Delegate 'System.Func<UnityEngine.Transform,int,bool>' does not take 1 arguments   

[unikronsoftware]

If you import this in Unity 5.1 it works fine - at least 2.5.4 does. Try importing tk2d into a new unity project and work out differences? That sounds like the most obvious thing to try here.