I keep running into this issue with Blender:
After rendering an image I select “Compositing” from the screen layout drop-down and sometimes I cannot add compositing nodes and/or view the render result as the backdrop.
When I try to add the output node everything is grayed out in the add node menus.
I have been able to correct this by clicking wildly out of frustation, but that of course prevents me from seeing exactly what I did to get it working.
I really appreciate any help here - thanks!