Time Remap expression not working when targeting parent.parent comp.

Question

I created a character rig and I'm trying to set it up so most of the keyframing is done on the main comp instead of the sub comps. Most of the body is set up in the main comp except the head which is in its own sub comp. In this Head_Comp, i have two more sub comps, SideHead_Comp, and FrontHead_Comp. In both of these comp i have the head base, eyes, eyebrows, mouth, etc.   The mouth is in its own comp set to time remap from the head comps.
Quick Breakdown:
Body_Comp
          > Head Comp
                         >FrontHead_Comp
                         >SideHead_Comp
                                        >Mouth_Comp
What I'm trying to do is be able to animate the mouth comp from the main body comp. I've done this with the eyes and eyebrows using dummy objects on the main comp, but when I try to "parent" the time remap of the mouth comp from each of the head comps to a slider in the body comp, nothing happens. The mouth comp will take the current position of the of the slider value and that's it, it won't change if I move the slider around. I'm doing it this way to avoid having a bunch of different copies of the head comps when I'm animating different scenes. I'm not exactly sure what I'm doing wrong.
Here is the expression I used.
a=comp("Diane - AE Rig").layer("Body_CTL").effect("Mouth_Control")("Slider")
framesToTime(a)
I've tried different expressions, but all it does is change to the current value and thats it. It won't move when I move the slider.
Thanks for any help.

Answer 1

If one or more of your subcomps doesn't start at time zero as a layer in its parent comp, you have to compensate for that. It's tricky with multiple levels, but basically you end up with something like this:
a=comp("Diane - AE Rig").layer("Body_CTL").effect("Mouth_Control")("Slider")
framesToTime(a.valueAtTime(time + some_offset))
Dan