The latest Chromebook update has caused an issue :(
Users will get a firewall message and won't be able to use Videostream.
We're currently working on a fix!
But there are two workarounds that other users have suggested:
a) Some users have said that when they start a video, a smaller Videostream window pops up. Exiting out of the smaller window and reloading the video seems to work.
b) When you receive the firewall problem using Chrome OS, please follow these steps in the correct order:
1) In the videostream white box (middle of screen), select 'reload and try again' button - note the button is greyed out initially and only becomes available for selection after a few seconds
2) When videostream reloads, in the pop-up videostream video box (lower right corner) - click the 'return to Videostream' button
3) Then select the video as you normally would using the 'choose a video' button when videostream reloads. The video should stream to your chromecast with no firewall problem.
Please let us know if this works for you!