Thanks for that link.

This thread should remain open pending resolution of the new problem with the player complaining that it needs a license.

I just noticed that the video player which is displaying the licensing problem is one which I have set to load an FLV file. Other places on my website where I use AllVideos to play a WEBM file are working normally with the "AllVideos Player." So I'm guessing that the AllVideos extension uses its own player for some file types, and JWPlayer for others. I haven't had time to look into this in detail yet. Hopefully someone from JoomlaWorks will be able to respond here.

Clappr is used as the extension's main player.
For formats which are not supported, like .flv JWPlayer is being used.

After updating allVideos to 4.8.0, I had the same problem with the invalid license key error. All videos on my site are flv and all display the error message. I had also just updated to Joomla 3.8.1. I have not updated my live site due to this issue.
- Steve

Sorry for the late reply Steve,

Can you try setting a new API key?
This post will help you get a new key support.jwplayer.com/customer/portal/articles/2339133