If there was a previous user record then it will need to be reactivated, rather than re-created.
First, check the Users list for Inactive people.
If listed then open, untick the Inactive flag, and populate the required settings.
If they are not there, then check the People list for inactive people.
Once found untick the Inactive flag, then go to the Users list, and click the +From Person List button.
This will need to be done because the Is Employee flag would have been unticked and might require the repopulation of some of the previous data.