I had a working system using ISPConfig that was fetching mail into dovecot and serving several websites.
I've been trying to recover an install of bugzilla so I've recently added a couple of bugzilla sites to my server and I installed Nagios to monitor my sites but everything seemed to still be working after these installs.
I wanted to be able to administer my databases from my work computer so I logged into MySQL and ran the command below on several databases (not the ispconfig database though):
mysql> GRANT ALL ON <db_name>.* TO root@'<my_ip>' IDENTIFIED BY '<my_root_password>';
This worked fine and I could manipulate the databases remotely, but my ftp accounts stopped working. It wasn't until the next day when I hadn't had any new mail that I realised it was more than just my ftp accounts affected so I went to the monitor section of ISPConfig and it says the MySQL server is down...which it isn't as I can still administer the databases.
I can't see why it stopped as it seems to have stopped at the time when I granted remote access to my databases but I didn't touch the ispconfig database and I didn't reset any other permissions I just added some new ones.