When connecting to the MySQL screens in DirectAdmin, if this error appears, that would indicated that the “da_admin” user has not been setup correctly.  Also you are reset the mysql root password too. To resolve this do the following.

/etc/init.d/mysqld stop
mysqld_safe --skip-grant-tables &

That should start up mysql without the need for a root password.  Once in, type

mysql
use mysql;
update user set Password=PASSWORD('newpass') where user='root';
GRANT ALL PRIVILEGES ON *.* TO 'da_admin'@'localhost' IDENTIFIED BY 'newpass' WITH GRANT OPTION;
FLUSH PRIVILEGES;
quit;

Now we need to make sure it’s setup correctly for DA to use.   Edit /usr/local/directadmin/conf/mysql.conf and set

user=da_admin
passwd=newdapass

Now edit the file /root/.my.cnf  and add the following lines

[client]
pass="newpass"
user=root