Error message when updating a username - message indicates that username is already taken

Content

Hi,

I am attempting to update a username in the system and I receive the below message (I used "xx" in place of the actual username). There does not seem to be another user with this username, so I am not sure why I am unable to change this. Does anyone know why this would occur? I am not super familiar with this aspect of the system, so I could be missing something obvious.

The username 'xx' falls into the block of accounts you wanted to add, but it is already taken. Unable to update user info.

Thanks for any help, appreciate it! -Jillian