OK gang, I have been struggling with sync issues between iTunes 11.x on a 2006 MacBook Pro running the latest version of Mavericks, and my iPhone 4S running the latest version of iOS (7.1 now). I finally fixed my problem, after literally months of frustration.
It sounds like folks in this thread may be describing somewhat different issues with syncing - not sure if they're all related or have common root cause, but let me first describe the issue I had, what I tried to do over hte past few months that didn't work, and then what I did to finaly resolve the issue.
Configuration:
As described, I'm using iPhone 4S (though I had same problem with my iPad Air) physically connected via USB to a 2006 MBP running Mavericks. I've kept up-to-date on iTunes versions, as well as iOS and OS X. For various reasons, I like to keep all my music local on my MBP, though I did use iTunes Match at some points over the past few months, so my library is synced (mostly) to iCloud. In iTunes, my sync settings were "sync music: selected playlists." My total music collection is larger than the storage on my iPhone, so I just want certain playlists, like my "recently added...."
Issue:
Around the time I installed iTunes 11 - but I can't exactly pinpoint when - I noticed that when I synced iTunes, the playlists would sync, but many of the songs in the playlists would appear with the dreaded red circle and square progress icon on the right. The songs wouldn't play. I could tap the red icon, and it would dim, but the song never downloaded. Strangely, song songs seemed to download just fine.
I even tried turning on iTunes Match and sycing. In this case, I would get the songs in the playlists (though inconsistently - not always all th songs would appear in a list), with the cloud donwload icon on the right. Sometimes I could download these songs, and sometimes I couldn't. Plus I clearly had some playlists that Match couldn't figure out so it just skipped them entirely and they didn't appear on my iPhone.
Failed remediation steps:
I tried resetting my phone (general: reset: reset all settings). Didn't work.
I tried erasing content and settings (general: reset: erase all content and settings), then restoring from my iPhone backuop with iTunes. Curiously, this didn't work, but after resyncing several times in a row, it worked, and I thought my problems were over. All my playlists and associated songs were there, available locally on my iPhone. However, the next time I tried to sync, it was back to square (and circle) one.
I finally broke down and made a Genius Bar appointment at the local Apple store.... Mr. Genius was actually quite helpful. He listened to my saga, and didnt even ask me to demonstrate the sync problem, despite the fact that I had lugged in my MacBook, the USB drive with my iTunes library on it, and my phone, just to prove to him that syncing didn't work.
According to Mr. Genius, this is actually a known issue. he's not sure if it's a problem that occurred only since iTunes 11, but thinks this may be the case. He explained that the problem is likely due to corruption of the iTunes library metadata that is stored locally on the iPhone. Unfortunately, in iOS, there is not way to selectively kill and rebuild the file that contains this data, the way you would expect to be able to do with a Mac or Windows config or data file. The only solution is to COMPLETELY rebuild your iPhone as a new phone, and make sure you don't restore it from a backup image. So, you erase all content and settings, and make sure you follow the directions to set it up as a new device. Here is the reference article: http://support.apple.com/kb/HT4137?viewlocale=en_US. The phone still retains your phone number. But all the data (apps, text messages, settings, emails, calendar data, photos, etc.) will be gone.
Once you've done this, you'll need to reconfigure your phone, and re-download all content. I had to download all my apps again (though the App Store keeps track of what you own, since you are signing in with your Apple ID), configure my email and calendar, etc. Then attach the iPhone to the computer, launch iTunes, click on the iPhone icon, and click on the music tab. Select sync music: selected playlists, and select the playlists you want to sync. Hit sync, and voila! It works (or it did for me). I've now had two weeks of "normal" syncing experience after this phone rebuild. It's a bit of a hassle to have to download apps again, organize them, configure mail, etc., but it's worth it.
Two things to know about this fi that are a hassle:
(1) You lose your text messages. No remedy to that, unless you use one of those third-party applications that allow you to extract text message data from your phone (I've used PhoneView for this in the past). This wasn't a deal breaker for me, but may be for you.
(2) Make sure that before you wipe the iPhone, you import any photos you may have on your iPhone camera roll that you haven't already imported. I forgot to do this and lost a bunch of my iPhone photos. Bummer.
But bottom line, after so many months of annoyance, it worked and I can actually sync my iTunes songs normally again.
Hope this helps some of you! Let me know if you need any more detail.
