Does anyone know what this message means?

The media server is what actually delivers the meeting to you. An issue with it could lead to lost funtionality or a complete disconnect from the meeting. I've not seen that message before, so I don't know what it could have been that the meeting was seeing to cause that issue. Sometimes the classic, close the room and relaunch it can resolve issues like this that may be something as simple as there was a failed or missed connection of your computer to the server.