GoToWebinar does not work in school - WS1100


Does anyone know how to get GoToWebinar working please?

The GoTo domain is not being blocked by the WS1100, but when staff click on any GoToWebinar "join Meeting" links in emails, no one can actually connect with any GotoWebinars. We tried downloading the GotoMeeting software, but that did not not work either. It's getting blocked either by the WS100 or the Internet providers Firewall, but I am not sure which?