I can't click on apps or see open apps on the remote desktop.

I have been using TeamViewer for years without a problem. Today, when I tried using it, I was able to see the remote desktop but when I tried opening Firefox nothing happened. I got a message which I attached above. I tried restarting my computer and the person using the remote computer tried restarting their computer. Nothing changed. My TeamViewer is up to date. I don't have a black screen. I can see the remote desktop, but I cannot click on anything. When the other person opens Firefox, I can't see it. I just see the desktop as if no apps are open. Why am I getting this message now? What can I do?