Thank you very much for looking into this and creating the sample. I looked it over and was at least able to narrow down the problem.
My Assignments list in my example is of type List<DataAccess.Status> and I am trying to convert to a different class, NewStatus.
That's where the issue lies. After running your example, which ran successfully, I ran mine again with the select of the linq query selecting a new DataAccess.Status and it worked perfectly. I originally noticed this problem, however, when running a groupby, which forces me to change that class type.
Could you please try creating another class with the same properties and selecting new of that class in the linq query? You should get a nullreferenceexception.