Your problem is not related to ip6tables, so you can ignore the messages you posted and ispconfig works fine in virtual enviroments, I use that on all of my servers.
Regarding your original problem, the problem is most likely caused by mysql or the hostname settings, so that the mysql client can not connect to the mysql master server.
You can check that by using the mysql commandline tool to connect from the slave to the master with the master server details from the file /usr/local/ispconfig/server/lib/config.inc.php
the mysql command is used like this:
mysql -p -h master.server.tld -u ispcsrv1 dbispconfig
the command will then ask for the password. Replace the hostname and user withe the ones from the config.inc.php file.