Changing host permissions for MySQL USERS

 If you've got access to the mysql database, you can change the grant tables directly:

UPDATE mysql.user SET Host='%' WHERE Host='localhost' AND User='username';

...and an analogous UPDATE-statement to change it back.

Also you might need to make changes to the mysql.db table as well:

UPDATE mysql.db SET Host='%' WHERE Host='localhost' AND User='username';

and then flush to apply the privileges:

FLUSH PRIVILEGES;