I called Apple and the rep said the problem was because I was using an old dock. He said that the dock slowed USB communications between the phone and my MacBook, and suggested I tried synching without a dock.
I did - same error.
But I figured out a better way - still annoying because you lose all your app settings when you update. Credit goes to
http://www.damienkomala.com/v6/unkown-error-on-the-iphone/ which I found mentioned in another Apple discussions thread on this problem.
1. Dismiss the error. Select the Applications tab from your iPhone in iTunes.
2. Chose "Selected applications" to sync manually.
3. Deselect the application(s) mentioned in the error message. This will remove them from the iPhone.
4. Sync.
5. Reselect the application(s) you deselected previously.
6. Sync.
All is well, until the next update.