The most common problem causing 'adding' button to be grayed out or hang is unreachable hosts. The backend Java library takes time to time out the validating request. Please give it some time if you have entered incorrect host name or IP address.
If the problem persists, please restart tomcat server by running `/etc/init.d/tomcat6 restart`.
If this doesn't solve the problem, double check your network configuration (wiring/switching/routing/firewall/etc) and make sure your host is reachable from I/O Analyzer controller VM via https.
You may also check the log file /var/log/tomcat6/catalina.out and see if JVM runs into any run-time error.
Thanks,
Chien-Chia