I planed to upgrade zimbra from 8.0.4 to 8.0.6, when trying to run ./install.sh, I got following error:

Operations logged to /tmp/install.log.31959
Checking for existing installation...
zimbra-ldap...FOUND zimbra-ldap-8.0.4.GA.5737.UBUNTU12.64
zimbra-logger...FOUND zimbra-logger-8.0.4.GA.5737.UBUNTU12.64
zimbra-mta...FOUND zimbra-mta-8.0.4.GA.5737.UBUNTU12.64
zimbra-snmp...FOUND zimbra-snmp-8.0.4.GA.5737.UBUNTU12.64
zimbra-store...FOUND zimbra-store-8.0.4.GA.5737.UBUNTU12.64
zimbra-apache...FOUND zimbra-apache-8.0.4.GA.5737.UBUNTU12.64
zimbra-spell...FOUND zimbra-spell-8.0.4.GA.5737.UBUNTU12.64
zimbra-convertd...NOT FOUND
zimbra-memcached...FOUND zimbra-memcached-8.0.4.GA.5737.UBUNTU12.64
zimbra-proxy...FOUND zimbra-proxy-8.0.4.GA.5737.UBUNTU12.64
zimbra-archiving...NOT FOUND
zimbra-cluster...NOT FOUND
zimbra-core...FOUND zimbra-core-8.0.4.GA.5737.UBUNTU12.64
ZCS upgrade from 8.0.4 to 8.0.6 will be performed.
ERROR: Unable to reach the Zimbra License Activation Server.
License Activation is required when upgrading to ZCS 7 or later.

The ZCS Network upgrade will automatically attempt to activate the
current license as long as the activation server can be contacted.

You can obtain a manual activation key and re-run the upgrade
by specifying the -a activation.xml option.

A manual license activation key can be obtained by either visiting
the Zimbra support portal or contacting Zimbra support or sales.

I tried to telnet to the license.zimbra.com

telnet license.zimbra.com
telnet: Unable to connect to remote host: Connection timed out

Please help.