Your router or firewall is blocking Altitude from accessing the Internet.
You must configure your router and firewall to allow traffic on port 27272 (UDP Protocol).
On your router, enable port forwarding and forward port 27272 (UDP Protocol) to IP unknown. You may find the detailed guides on portforward.com
helpful - follow the link and search for your router model. NOTE: portforward.com is in not affiliated with Nimbly Games, LLC.
On your firewall, create a rule that allows Altitude to send and receive data on port 27272 (UDP Protocol).The following has instructions for the default Windows firewall.