expression error

I have an expression error after I've pre-composed. The error states that one of my layers is missing. It's a layer that has 5 opacity keyframes. It says it may have been mis-labeled or a typeing error or something like that. After I pre-composed, I viewed the animation and the layer is there and it's seen within the animation. I don't understand what's going on. When I open the layer, underneath the opaciy of transform, there is an expression written (code I guess). What do I do?