That link says that it is a trust issue. You can "unblock" the DLL (via file properties) and then it should register.
The XML delivery channel does not have an owning assembly, as it is not a support assembly itself. I would suggest that you recompile against .Net 3.5 - this issue about registering support assemblies has cropped up before, and I've seen answers in a couple of other discussions in these forums. See this [DEAD LINK] thread as a starting point.
Greg: Pls wait until someone from the Notif. dev team can comment.