"The file 'x' could not be copied because this computer is not authorized."

I am trying to get an app (VSCO Cam) from my sister's iTunes library. We are logged onto the same home share network, and I can open her library just fine, but when I click the app and click "Import", a box shows up and says, "The file "VSCO CAM could not be copied because this computer is not authorized." I'm not sure wat computer it's talking about, buton both computers we've got up to the "Store" button, clicked "Authorize this computer", and we've entered OUR OWN Apple ID's. Now, the one we use for homesharing is different, and we both have our own apple ID's, which I put in my own, and she put in her own when asked to authorize our computers. Should we be putting in the ID we use when we homeshare when asked to authorize? Or will that change everything about our iTunes libraries.

I can import a song just rom her library just fine, it's only when I try to do the app/.