Contacts and Mac OS Address Book won't sync anymore
I have an iPod touch, 2nd generation, with iOS 4.2.1, which has worked perfectly well for years.
Since I got an iPad 2 with iOS 5.0.1, and iTunes 10.5.1, and set up iCloud, and synced the iPad to my Mac, now my iPod touch will no longer sync any address book entries between iOS Contacts and Mac OS X 10.7.2 Lion's Address Book.
I've tried restoring the iPod touch to its factory-fresh setting and syncing with the Mac. I've tried rebuilding the Mac OS Address Book index, and repairing permissions on Mac OS X. Nothing seems to help.
Another clue is that the iPod touch Contacts stopped syncing at 512 Contact entries, while the Mac's Address Book had 521 entries. I think 512 is a suspicious number; is it an upper limit on entries that sync with iTunes and Address Book?
Any help would be appreciated.