I have linked my Mojang and Twitch accounts, but when I try to to stream, the message attached appears. I have restarted my Minecraft and restarted my computer repeatedly, and waited several hours, to no avail. I have previously created a Twitch account and linked it to my Mojang, and streamed successfully, but later deleted it and linked it to my new one, with which I am having issues with. I will provide more information upon request.
It may possibly involve other versions than above, and it my not be server-side but client-side.