The slave is not able to connect to the master database, so it can not fetch changes or update the status. The most common reason for that are wrong or missing entroies in /etc/hosts on master and / or slave server. It is important that all servers of a cluster have all other servers in their /etc/hosts files and that only the fqdn is listed there as it is decribed in the multiserver guides.
You can verify this by trying to login on the commandline from slave server to master with the mysql master login details from file /usr/local/ispconfig/server/lib/config.inc.php
As you most likely dont want to reinstall the slave if the hosts were wrong during install, you will have to fix the hostname of the ispcsrv[ID] mysql user of this slave in the mysql master database.
The other, on ISPConfig > Monitor > Overview, it shows (Debian Wheezy/Sid) ISPConfig 188.8.131.52 beside ns1. ns2 however does not have ~anything~ beside it's name.
Thats related to the connection issue.