I approved a user, then quickly realized it was a spambot.  Deleted the user and this is what is at the bottom of the main forum page:

The newest registered user is Guest

When you click on the "Guest" username/hyperlink it goes to:

Sorry, but that user does not exist.

Any input for this one?

Ask someone to create a new account or create one yourself ...I think that would be a quickfix  

clear cache.

or go to your db

look for users_table and check for the last entry

I cleared the cache and ran most of the DB tools prior to posting this thread.

I did join myself as a test user and emptied the cache again, then deleted the test user and the same problem has come back.

I'll have some time to check in to this a little further this weekend.

This issue is very strange... which version of Icy Phoenix are you using?