2d layers break the rendering order. Move that 2d null out of the way. Your shadows are being cast onto the lines, if you'll notice, so that Null Control layer is messing with you.
Ok! You think that's happening even with the Null being turned on 3D? Also, when you say to move it out of the way, do you mean just move it below all the layers?
Wait, if the null is a 3d layer, it should work - I think I was getting thrown off by the motion blur switch (it's been a long day; Daylight Saving Time is a dumb idea).
Now, you are getting shadows from your lights. I see shadows on the connecting lines. I just don't see any shadow on the background. Double-check the background's position in relation to the other elements.
Any chance you could share your project file so I could poke at it?
Here's how I diagnose things. First I select the layers I'm having problems with and press the U key twice to reveal all modified properties. In your case I soloed a point light, the background and one of the circles then gave things a quick look. To make sure layer order wasn't causing problems I moved all 3 layers to the top, moved the circle away from the background a bit and then picked two views and started turning effects off first one at a time. When I got all of the sliders turned off I found that the shadow magically appeared.
I haven't taken the time to dig into the expressions and figure out what they are doing but that's where your problem lies. Any one of the sliders turned on will turn off the shadow.
Your light position doesn't make much sense either. If the shadows were working because the lights are so close to the circles the shadows will be flying all over the place.
You also don't need to apply Drop Shadow if you are using lights to cast shadows.
Thanks Rick! Yep, those sliders are from a script I bought from Mt. Mograph... I was wondering if those might affect anything. I'll have to email him about that for the next update.
I appreciate your tips for diagnosis as well. I'll try that next time before posting on here about an issue.