I attempted to upgrade (clean install) last year to El Crapistain and iTunes 12.2.3 or higher. However, one major issue held me back: with every version after a clean install, iTunes eventually no longer allows me to do anything where a login prompt is required. I can go to iTunes Store, but if I click on Account or anything else that wants my credentials, no login prompt will come up. As a result, I can signin, authorize or deauthorize my account on the computer, buy anything, etc. As a result of this, I downgraded to 10.10.5 and I don't have any of these iTunes login issues--it is only on iTunes 12.2.3 or higher and El Capistan. I do some mobile development tinkering and now that Xcode 7.3 only works on 10.11.x, I would like to upgrade. I have had this problem--and tested it--in each version from 10.11.0 - 10.11.4 and it is still there for me. Typically it works for a while but then, without any software changes, it stops working within a week or two after a clean install. Note that I use iTunes for my own local music (no Apple Music service), podcasts, iTunes U and iOS syncing with no iCloud use or backup. I have tried quite a few things and none of them have worked--I have tried: Create a new OS account--still can't login to iTunes Delete existing OS account and recreate it--still can't login to iTunes Create a new iTunes account--still can't login to iTunes Delete all iTunes preferences--still can't login to iTunes Delete all Safari preferences, cookies and website data--still can't login to iTunes Logged into iCloud (even though I don't use it for anything on my Mac)--still can't login to iTunes iTunes working properly is critical to me--if I can't get it to work, I will stay on Yosemite until my 2013 MBA dies.