Take 2!! Motion Title Project: Applied Mask turns bkgd black

This is a re-post...I am so sorry this originally posted under a different profile name (I didn't even know I had! Go figure!) and I wanted you all to know it was me!

Hey Everyone!

It's been a little while...I've been learning, learning, learning! Tutorial after tutorial.

I'm doing a tutorial that has given me a project file to continue the lesson with. I could (and probably should) just use this already built project file and move on with the tutorial. I'm sure that's what most people do. But I figure - how can I learn anything like that? I should try to rebuild the project myself and when I get stuck use the already built project to help me out. Right? :)

Here's the thing. This time what I've rebuilt (so far) doesn't quite look the same. I've poured over both projects comparing each and every little detail. For all intents and purposes it is an exact duplicate. Except it's not. I'm really thinking this is some kind of easy fix that I just don't know about and can't find in any of my research. And I'm going to probably feel pretty silly once you all clue me in. But I'm willing to risk that for the sake of learning! ;) So here I am to ask you great folks...what am I doing wrong?!!

Background: This is a Motion Title Project. I am applying a mask with a link behavior so that when the ball rolls across the screen it reveals the graphic and text behind it. It does what I want it to do, so yay there!

But once I apply the mask the whole background turns black. Invert the mask and of course the opposite happens. The background turns gray like I want it but the masked area is black. I have poured over this thing multiple times comparing the two projects and just don't see what is different. Finally as a last resort here I am to bother you all with it.

Any thoughts, ideas or just overall wisdom to share? My many thanks as always for your time, help and support!