As a general rule, if there is a problem with connectivity, open up all TCP and UDP ports between 9600-9660 inclusive.
Warning
While it is possible to use Intelli-Site from location to location across multiple subnets, it is not recommended that external firewall rules be modified, but instead a VPN connection created between the sites.
Warning
Opening ports in your firewall can be dangerous and lead to security issues, it is best to avoid opening ports that are not in use. Contact your IT professional for more info.