Join Date: Jan 2009
Location: Guelph, Ontario
Apparently there has been some chatter on the Apple Support site about this issue over the past couple of weeks. No clear pattern as yet (with little to no help from Apple support), but may only be on Windows. I am running XP on both machines so it is not a Windows 7 issue.
I am never prompted to sign in, and previews have always played until now. It must be some problem with iTunes that they are hopefully working on.
Edit: It is working normally now, knock on wood.