Hi, could you please run the SQL strings below in your current database and provide the query result to us?

SELECT *
FROM [$DATABASE].[dbo].[cf_users]
WHERE username = '$Username1' 
OR username='$Username2'

SELECT *
FROM [$DATABASE].[dbo].[cf_usergroups]
WHERE full_group_name = '$Username1' 
OR full_group_name = '$Username2'

Replace '$DATABASE'  with the database you currently use. Replace the '$Username1' and '$Username2' with username of the two problematic accounts respectively, which can be grabbed on Administration page.