I was trying using gotowebinar to join a public webinar but when the session started the slides windows showed the message "sorry, this portion of the webinar cannot be viewed on your device" with a black background. I was using Windows Server 2012 R2 Datacenter as a Google Compute Engine Virtual Machine. Knowing that I viewed another webinar before on the same VM
In some cases you may see that message where your device does not support the way GoTo streams videos. This is not related to desktop / application sharing or webcam sharing, but specific to videos the Organizer has queued up in advance of the broadcast.
Can you let us know if this problem persists, and if you were joined via the web app, or desktop application?