Jennifer
You are not alone!
I have had this for a while now, but no luck sorting it at all. I am using DNN4.6.2 though, and have setup a clean test installation and database here -> http://208.106.211.27/ which has the exact same problem.
No users get notifications, apart from a blank notification on deleted posts. If it can help resolve the problem, any volunteers/interest parties are welcome to admin access to see the settings.
Hope we can find the problem... and a solution!
David
PS. I don't even get notifications from DNN's forums!