The 'Correct Answer' as posted by LockerGnome is not the correct answer, at least when a PC is involved, as I have been able to reproduce the error afterwards. It only fixes the problem temporarily. How do you change its status?
This is how I was able to reproducet the "1 item could not be synced" message. I don't know if everything is a prerequisite but these are the conditions:
One iPHone 3GS 32GB fully up-to-date, with iCloud, photo stream etc., all activatd.
One Windows 7 64bit PC with iTunes 10.5, all up to date, photo stream etx. active.
* The iPhone and PC must previously have been set to sync with each other, over-the-air syncing may or may not be a prerequisite.
* iTunes should be set to sync photos from the PC to the device. It may be a prerequisite that only certain subdirectories of the Pictures folder are set to be synced.
1) Press the home and the unlock/on/off button on the iPHone together to make it take a screenshot.
* Taking a photo may also work but I haven't tired this yet.
2) Wait a few minutes for photo stream to receive the picture.
3) Launch iTunes on the PC.
4) Select the iPhone in iTunes.
5) Press sync.
6) Wait for the sync to complete.
These things will happen:
* All the photos that are set to be synced from the computer will be uploaded to the iPhone, even if they haven't changed.
* At the end of the sync, the iPhone will display the message that items could not be synced, and to check iTunes for details.
Also, there is no additional icon iext to the iPHone that you can click on to find more information. Perhaps this icon only appears when syncing via wire.
UPDATE: The above steps were not enough to reproduce the "1 Item could not bye synced" bug. There was also an iCloud backup, perhaps this is also required. I'll let you know when I have this figured out.
In any event, all the photos still get downloaded from the PC to the iPhone, so I guess this is a reproducable bug.
I just got the 1 item could not be synced message again.
The following things happened between yesterday and today, any of which may be pre-requisites for the message to appear:
a) An auto backup to iCloud took place
b) Updates to some apps on the iPhone took place
During the sync, the updated apps were transferred from the iPhone to the PC.
Here is a picture of iTunes after the sync. This shows another problem: the iPhone is plugged into the PC and the iPhone displays the green battery screensaver whenever required, but the power icon that should be next to the eject icon (circled) is missing. Also note that there is no additional icon, as mentioned in a previous post, that may indicate the additional details of the error.
I have gotten that same error message every time I have sync'd my 4S, and every time on my ipad since updating to 5.0. It sends you to itunes for an explanation, but there is no error message on iTunes. Of course, it is not as serious as the battery issue, or even as serious as the problems with the new Music app on the ipad (crazy, huh)? but still another major flaw. Doesn't anybody test these things before releasing them???
I've found the item that cannot be synced. It's an expired rental movie that still appears on my iPhone. However, every time I delete the movie, and do a sync, it comes back. I've tried differernt things but the deleted movie always comes back.
Here is the deleted movie.
Note that the movie expired months ago.
If I delete the movie, and click apply, the movie goes away. But if I click Sync, it comes back.
If I select set up iTunes to sync movies, or to not sync movies, this doesn't help. If I set up iTunes to manually manage music and videos on the device, this doesn't help either. No matter what I do, the movie always comes back.
Resolved my sync issue by first backing up my phone using both as a local backup and to iCloud. Then issuing a reset and having all my settings erased, then choosing to restore using iTunes from the phone. After my restoration was finished, I still had the error about ## items could not be sync'd but upon removing all photos from my phone, deleting the photo cache, and then resyncing them, I no longer got the error anymore. All my photos were there, all album art that were previously missing are back, and all my settings were restored such as contacts, saved passwords, etc.
Before going through deleting all cache files as LockerGnome suggests, there might be a far easier quick fix.
I had 85 items being not synced every time I hooked up my iPad to iTunes (normally the syncs go over WiFi without the error message). I remembered having added a large number of video files to my iPhoto library lately. I also noticed a strange behavior of the 'capacity' bar in below the iPad section in iTunes that would constantly increase with about 8GB after hitting the sync button and dropping the same amount when re-attaching the iPad. This indicated to me the 85 files must be big, ergo video.
I went to the Photos section of my iPad in iTunes and disabled the 'Include videos' option at the top. Sure enough the capacity bar stopped jumping 8GB and the error message disappeared from my iPad after syncing.
NB. The videos selected in the Movies section are still on my iPad. I guess it has to do with the (kind of) video files that are synced through the iPhoto library.
I had the same problem and this fix has solved it.. Except I had to press the X in the iTunes sync box for the iPad as it tried to bring in 25GB of iPhotos.. I wanted only one Album set.. So you need to watch what is happening in Photos part of iTunes. Then when I put my iPhone to Sync it had lost all the photos and iPhoto sync was turned off. So I had to replace photos by reimporting.
I think there may be a number of underlying issues, but I found a solution that worked. I had an iPhone 4, and just upgraded to a 4S last week (iOS 5.01 was installed on the iPhone 4 before the upgrade and I was backing up to iCloud). I did a restore from iCloud when I got the 4S and discovered yesterday that I had hundreds of songs that would not play. I don't know if I had pictures that would not sync because I did not check them all. I tried removing and resyncing the music, and also did a full backup to iCloud and restore last night....no luck. I also tried deleting the photo cache, moving the problematic songs to a new playlist, etc. None of it worked. I was still getting the "320 items did not sync. See iTunes for information." error....of course, as others described, there was no information on the error in iTunes. So, here is what worked:
1) I set my device so that no music or photos would sync
2) I did a backup to iTunes instead of iCloud.
3) I restored my 4S from the iTunes backup
4) I added back my playlists
5) I added back my photos
Everything works beautifully now and I restarted iCloud backup. Steps 1, 4 and 5 may not be necessary, but I thought I would go through those during the process just in case they helped.
What worked for me was to go to itunes preferences, then go to "advanced" and then click the buttons "reset warnings" and "reset cache." this works like a charm.
NOTE: i had deleted the file that "could not be synced," but for some reason, the phone kept alerting me about it, even though the file was removed from my itunes account. This method above worked to resolve my issue, but you may need to remove/redownload the corrupted files to actually make the warnings go away.
When your phone says that "n number of items could not be synced," go and open itunes on your computer. It should list the problematic files. If you already know what song/movie/photo is corrupt, go to your library, and try to play it on the comp. It should say "file cannot be played" and a gray exclamation point should appear to the left of the song title. Then, you can delete this file by right clicking it and choosing "delete." hope this helps