MariaDB 'You do not have privileges to manipulate with the users!'
Can you login with a command line client? (just to have a more clear picture of what is happening)
If yes :
   What does "select user, host, db, select_priv from db;" tell you?

Are you able to start the database with the --skip-grant-tables option?
If yes :
   Now have a look at mysql.db and mysql.user to check permissions.

-- EDIT:
Just wondering: Can you do something like :
grant ALL on . to ''@'';
grant ALL on . to ''@'localhost';

I have the feeling your user lacks the appropriate permissions.
(If the above works you would probably be able to do more with 'your_user' now.