This is a sharp edge in TBB that people will cut their fingers on: task_group_context undefined. It took about half an hour to figure this out and I am writing here to suggest that someone take the time to find a better way to inform people when they hit this problem. This occurs when you have failed to turn on C++ Exception Handling.
To fix: Options/C++/Code Generation and turn on C++ Exception Handling.
Hope this helps someone.