After iPhone 5s upgrade to 8.3, iTunes will not sync calendars to iPhone

Have iPhone 5s sync'd to iMac running MOS 10.8.5.

Calendars sync'd fine between iMac and iPhone until iPhone version upgrade to iOS 8.3.

Now iTunes 12.1.2.27 will not sync calendars.

Error message says "SyncServer" cannot sync Calendars with iPhone.

All applicable software is upgraded to current.

Have tried multiple restarts with and without iPhone on.

Also discussed with Verizon Tech, who wanted to trash "Calendar" app. and reload, but did not know how.

Have seen community notes on similar Windows-based problem related to SyncServer file.

Made changes in iTunes Playlist and they sync'd fine to iPhone.

As far a I can tell, everything else on the iPhone works fine.

Any solutions/suggestions would be appreciated.