Quit and reopen iTunes. If the issue continues, then restart your computer.
Quit iTunes, temporarily disable the anti-virus security software on your computer, then reopen iTunes and try to sync your device. If iTunes successfully syncs your iPhone or iPod touch, consult the anti-virus software vendor.
Turn off Genius in iTunes in the Genius sidebar (choose View > Hide Genius Sidebar).
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This document will be updated as more information becomes available.