If you installed a ispconfig multiservers etup, then the info should get synced automatically between the servers. If the sync dont work, then you can debug it with the instructions here:
The most likely reason for your problem is:
1) You changed the mysql configuration of the master so mysql is not listening on all interfaces anymore.
2) A firewall was started on the master server which blocks the mysql port.
3) A hostname or IP address of one of the server ahs been changed or the /etc/hosts file does not contains the information for all servers of this cluster.