The iTunes on my secondary computers (i.e. the computers I don't sync my iPod and iPhone to) are now prompting me twice to 'log-in to my iTunes account to enable automatic downloads' before I can play any music - first when I open iTunes and again when I go to actually play a song. While I have music in iTunes on my non-primary computers, I don't need or want them to be connected to my overall iTunes account - I buy almost nothing through iTunes and just don't want or need them to be connected.
This is the box that pops up twice (that has somehow autofilled my email address even though I've never used the account on this machine's iTunes):

I checked system preferences and didn't see anything that would appear to disable the pop up, but anyone know how to get rid of it?
I realize this is a fairly basic question but it's super annoying. Both computers this is happening on are macs, if it matters.
EDIT: This is what the Store Preferences page looks like - I don't see an option for disabling downloads, only ways to enable it via an iOS device or to a different account.

