Hi keletso,
Hope you are doing good.
This is indeed very strange. Just check the "LOCK" button in /nSU01. Try to isolate the issue by changing the user type to "dialog" and see if you are able to login to the r/3 server using this user.
If the issue persists, it would be better to check the actual engine;can you raise an incident with us and we can login and check fast.
Regards,
Hemanth