This query concerns Adobe TV but can't find 'help' on this topic.
Using Firefox V39 on Windows 7 64 bit
Tried running an LR video on Adobe TV and the video 'failed to operate' (blank video box).
Thought "OK, must sign in" and the video ran.
Chose a second video and again the video failed to run.
After messing around a bit signed out and the video ran.
Chose another video - no joy.
Signed back in once again and presto it ran.
This effect has been repeated 5 or 6 times now.
Try a different browser.