As of 4.3, cameras will not render projectors unless they also render the layer of the object being projected onto.

1) Open the attached project in Unity 4.2
2) Open the test level
3) Observe in the game view that you can see a cube (being rendered by Main Camera) in the middle of the scene; observe that the blob shadow (being rendered by Camera) appears above it
4) Open the attached project in any version of Unity 4.3 or greater
5) Open the test level and observe that the blob shadow is not rendered at all
6) Select the Camera object and add the Default layer to its culling mask; observe that it now renders both the cube and the blob shadow

Regression since 4.2

Closed as By Design because:
"This is caused by the fact that projectors now use the visible lists from the main scene as input, which makes them work with occlusion culling etc.

However it means any layer culling from the camera also applies to the projector.

Object has to be visible to camera (not culled by the culling mask) in order for projector to project onto it.

This is more consistent/logical behavior than it used before (prior to 4.3)"