I am in level 19 (water torture). When I approach the elevator with the red card key the elev. door is already open. When I use the red card key the key pad changes green but nothing happens. I have tried replaying the level. Nothing changes.
Paul

I am also stuck on level 19 but with a different issue. After I break the window to flood the room and retrieve the red key card the red card reader disappears. I cannot use the card to open the door and drown every time. This is a major glitch. The card reader just disappears. WTF

You'll need to exit out the now broken window and get back into the base another way.

I have an adjacent issue: once I got down the red-key elevator and got the green-key, the elevator won't go back up. I looked for switches, stood on it, nothing.

Try pressing the 'use' key anywhere while standing on the elevator, if you haven't already.