I don't really understand what you trying to do.
An invisible block is invisible, how can you cast
shadow on it?

As you said you have 2 mdls : one player and a scene?,
I think the scene is a ground model. If you want to cast
the player's shadow on the ground then add a large block
which is almost the same size of your ground model then
move it under the ground model as close as possible, then
swtich on stencil shadow as I stated above.

If this is not what you want, I think you better post some
screenshots or codes and describe more clealy what you gonna
do exactly.

EDIT
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It's much better to post it to "Starting with GameStudio"
and you'll find more help.