An error on the sync log reads:
"Validation Exception was thrown.Details:Business Validation Error: Unexpected user error. ( -12476 )"
Cause / Solution
Cause: This error is caused by having a Preferred Vendor set to the problem Item.
Solution: Remove the preferred vendor by navigating to the Item page for that particular item. Click the vendors tab and hit in the delete button to the right and the sync should go through the next time around.