Shadow only inconsistant.

sometimes I can get it to work, other times not.
These are checked:
Shadow only - on floors’ mirror transp tab.
traceable and shadow - on floors’ shaders tab.
traceable and shadow - on casting objects’ shaders tab.
buf. shadow - on spotlight.
only shadow - on spotlight.
I can still see the whole floor when I want shadow only.
What am I doing wrong?
Never mind. I neglected the 'shadows button in the render panel.
( And I pulled out my hair just for that !??? )