Newbie experiencing "property already referenced" error

[scGroove]

Trying to set up a reusable, dynamic, lower-third template in After Effects, I'm receiving the following error: 

After Effects warning: Property is already referenced by a controller and can only be refrenced once.

I know what this is referring to ... I'm trying to add the "Scale" property into the Essectual Graphics window twice. However, it would seem to me that you can do this provided the second instance references a different layers contents. You might need to ba able to adjust scaleing on more than one object when the template is used in Premiere.

A little background on this ... I am just following along on a Shutterstock tutorial and imitating what I see done in the video. Only when I do it, it's throwing the mentioned error. There must be something I'm doing wrong, but beeing fairly new to AE, I'm scratching my head on what's going on here.

You can see the instructor do the exact same thing in the video. At 9:29 he drags up a "Scale" poperty from the lowest layer called "BG". Then, seconds later (at 9:34) he successfully drags another "Scale" property up to the same window from the next layer up called "BG Matte."

How can I also get an adjustable "Scale" property from my Background Matte layer?

How to Make a Lower Thirds Template You Can Use Anywhere 

[Rick Gerard]

You have to solo supported properties and drag them to the EG Panel. If the properties are in a nested comp (pre-comp), you can open the pre-comp and solo properties again. Then you just have to give them appropriate labels. You can also add a null to the Main comp and add effects controls like Sliders or Point-controls.

Without seeing your timeline or taking time to go through the entire tutorial, that's the best I can offer. 

[scGroove]

Thanks Rick ... and sorry for my delayed response. Been very busy at work. Below is the timeline. You can also see the Essential Graphics Panel. I've already dragged up a scale property from the very bottom "background" layer ... that's the one you already see in the EG panel under the "Backer Box Settings" label. The error that gets thrown is when I try to drag another "scale" property except from the layer just above it called "background matte". Thanks for you assistance.

[Rick Gerard]

The Background Matte Scale is right at the top of the EGP. That is why you cannot add it again.

You can rearrange the order of the controllers and edit the names.