This means that when you're doing a call like
from a background thread and you get a NullReferenceException on that line, the exception may originate from inside the target method specified by the delegate. That is - on the foreground thread.
In my case, the method called by the property called by the method called by the target method of the delegate was the ultimate culprit. I think I may need to start sprinkling in some try...catch statements, at the very least in the target method...