Ric Trexell wrote,on my timestamp of 31/08/2008 1:31 PM:

camera when not in use. The thing that has me puzzled is that I expected it
to be like the little door on a floppy drive in a computer that moves out of
the way when it is inserted. Nothing seems to move and I was wondering if
something had to be moved like a lever or something. Perhaps mine is frozen
or stuck. I will look it over closer but I might have to take it to someone
that knows what I'm doing wrong. Ric.

There is no door whatsoever. If you have a late model Pro-s back,
there is an interlock that won't let you remove the dark slide
unless the back is mounted on a camera. That is to stop you from
removing the slide and accidentally exposing the film surface.
You can only remove the DS when the back is mounted on the camera.

Should be same for putting it back, but have never tried it outside
the camera. The interlock is a little tab on the edge of the back,
but my advice is to leave it alone. The reason there is no door for
the slot is that the slot itself is lined up with light baffle
material that won't let light in but will let the DS in and out.

HTH