Usually, when you see this error, it is because your IT department has a firewall enabled that is blocking port 22, which is needed to allow your computer to talk to the server. The easiest way to solve this problem is to have your IT department add an exception to your computer. Ask them to add exceptions or whitelist the following host names:
If you need to know the IP addresses for these host names, you can do a
nslookup lookup (for example: http://ping.eu/nslookup) to find the current address.