How to re-enable background transparency (Blender Render)? The 3d object below has a grey background. It should be transparent though (which is the default setting).
But somehow this is gone.

I'm using Blender Render.

Can you point me to the checkbox I need to click to get it transparent again?
Drop down under Properties/Render/Shading/Alpha. Although you seem to have a special compositing setup so it might be a different issue.