I am assuming that the first operation (Register User tool) correctly added a person document to the address book. My guess is that what you saw was simply a caching delay; the view that is used by the selection box had not updated to include the new person. If you see this behavior again, try pressing CTRL+SHIFT+F9 while the address book is open. This will update all the views. Then try the selection dialog again. If this does not work, write back.
This was first published in July 2003