If you receive the error 'Export was complete but with errors and should not be used
' when exporting all data to a CSV you should open the file with a text editor and search for the word ERROR to see the fault lines.
If the there is only 1 line
and it starts with...
... then this is an old user record that has not been updated in your database. You can import an update to this users record by importing this CSV file
. Once imported into your database you should be able to export without error.