If the ceiling refuses to move, then try:

If the ceiling won't extend, try clicking retract, then try extended ceiling again. If the ceiling won't retract, try clicking extend, then try retracting ceiling again.

Now try clicking “Emergency Stop”. Now try either above steps again.

If that doesn't work, now try going to the big grey box at the back of the CAVE. Click the power button to turn it off. Wait about a minute and a half, then click the button to power it on again. The ceiling should hopefully extend now.