"User name not found in the Name and Address Book" came up when a system that had not been changed was used. The code was sending email and failed on the lotusscript doc.send line. The users' connection documents and setups were checked. It only affected some users.

The problem was a corrupted view in the Name and Address Book.

It was one of the $VIM views.

Re-saving the views and replicating the database solved it.