Administrator or Co-Administrator can get the message "This user already exists. Click 'Add to account' to add to your account" while registering the user in User Management.
This situation can sometimes occur in scenarios, where:
Click "Add to Account" hyperlink in the modal window and finish the user registration.
If you are unable to add the user, please contact licensing support using one of the following methods:
Unable to add users - user already exist within another ultimate
Auto Approval set-up
Other Language Sources