Mac App Store not working

[meeperson]

I just updated to Yosemite, and when I try to install Apple's updates for GarageBand, iMovie, and some other things the App Store tells me I need to log in to download updates. However, I'm already logged in and it won't let me change the Apple ID in the login window that pops up to mine. I checked that I was logged in, restarted it, logged out, logged in again, and it's still not working. Please help! Thanks!