Today I had a strange problem with VSTS 8.0.50727.42: I could not add a new data source of type 'object' to my Windows control library project. Adding a database or web-service data source worked fine.
The wizard would crash when trying to open the 'Select the object you wish to bind to' page of the wizard. The error message was this:
An unexpected error has occured.
Error message: Object reference not set to an instance of an object.
If I made a new Windows control library project and added classes from my business entity assembly as object data sources, the wizard worked as expected (kind of stupid that several classes cannot be added in one go, though). After several hours of experimenting with project references, structure, and even names, I finally saw the pattern of when the wizard worked and when it crashed. The wizard is dependent on your project having at least one public class in the root folder of your project.
In my Windows control library project I have structured the source code into several folders with no classes in the root. VS by default generates a class called 'UserControl1' in the root, and if you delete this class, the wizard will fail.
I now use a dummy class 'XDummyClassForDataBinding' in my project.