Recent changes in Norton Internet Security Anti-Virus have been found to cause issues with SwizzSync. This is due to the Automatic Scan settings in Norton. This can be quickly resolved by unchecking the 'Scan files located on external drives when accessed' option in Norton.
Open Norton and click the Advanced/Customize option at the bottom. Then click the settings icon next next to Automatic Scans.
Next, on the Automatic Scans window that opens, uncheck the 'Scan files located on external drives when accessed,' and click Save.
This should prevent issues from arising due to drive scanning by Norton.