Looks like there’s a bit of a bug in iTunes 8, with fairly widespread reports of iPhone syncing errors.
After waking up this morning to a dead iPhone, I plugged it in for a quick blast of juice. An error popped up on screen, saying that my iPhone couldn’t be synced. An “Unknown error occurred (13213)”. Unknown error? Nonsense! I poked around the googletubes a bit, and everyone was just saying “turn the iPhone off, restart iTunes, and then plug the iPhone back in.” Been there, done that. Three times, in fact. Still nothing.
So, I thought about the only thing that had changed since it last worked. Right before I crashed for the night, I was playing with the new Genius feature for the first time. Turned it off, and pow! iPhone synced like a charm. I was able to turn it back on without any issue.
If you’re having issues syncing your iPhone or iPod because of “Unknown error (13213)” and the standard power cycling/iTunes restart doesn’t fix it for you, try switching Genius off. To do so, just go to Store > Turn Off Genius.