Q: Garageband was not able to install the new sounds

I'm on an iMac 21.5-inch (mid 2011) running Yosemite; 2.5 GHz Intel Core i5; 4GB memory.

A few months ago, I uninstalled GarageBand. Now I'm trying to reinstall it. I can get GarageBand 6 reinstalled, but I would like to get working with the latest version. I'm able to download the latest version from the App Store with no issue. It installs with no issue.

When I open it, it thanks for me downloading it, and then begins to download "an essential collection of sounds and loops." After a bit of downloading, it asks for my admin password; I enter it, and a few seconds later, it gives the error: "GarageBand was not able to install the new sounds. Close and re-open GarageBand to download and install them again." Closing and reopening GarageBand just takes me through the same loop (no pun intended). When the window is open, if I click on the GarageBand menu in the Apple bar, nothing happens.

It does not ask me to accept anything; I am signed into the App Store with the same Apple ID I have always used (it is the only one I have ever had, so that's not the issue). I am an admin on my Mac, so it's not a permissions issue. It's not a password issue either.

Things I have tried:

• Rebooting into Safe Boot and opening from there; same issue.
• Repaired permissions (it fixed oodles of things completely unrelated to GarageBand); same issue.
• Creating a new admin profile and opening from there; it gives a different error, but the effect is the same.
• Removed the program, trashed anything remotely related to GarageBand (preferences, folders, etc), emptied the trash, restarted the computer, reinstalled; same issue.
• Installed GarageBand on top of itself, just in case; same issue.

I can't think of what else to try. Help!

For reference, here is a screenshot of what I'm getting stuck on: