Insert the tray-all of it except the grounds container. The message disappears and you can wait until the machine continues it's cycle and then asks to empty the tray. Empty the tray and place the grounds container back inside. Whew, I've done this a few times over the years when I am rushing but it fixes it every time.
Just fixed this same problem by taking apart the water solenoid valve and cleaning out its connection tube of deposits that was blocking water/steam flow. I removed the magnetic coil but that's not required. The connector was very tight because it had loctite sealer on the threads. I used plumbers teflon tape on the threads when reassembling.
It is possible that the timer unit in the maker is defective and need to be replaced. I would suggest you move the coffee maker to a different outlet and see if you have the same problem. If there is a short in the mechanism or a bad connection in the timer it could be experiencing a thermal shutdown.
For Jura F7 Series, "Tray Missing, can't put it back in". With a small flashlight, look in to the cavity which the tray and grounds container reside in. Along the right side above a slot to the end, you'll see a white micro switch. with a "Tooth Pick" simply press the switch inward (to the right) and hold till the machine cycles the Levcer / Flap up and out of the way.! Put your tray and grounds container back in and begin brewing!! -dh