Internal Server Error - Read The server encountered an internal error or misconfiguration and was unable to complete your request. Reference #3.35f90a17.1503594967.1bf3cb1e

Hi, I am trying to make a backup of my i-phon 6 on my MacBook Air in order to get the data transferred to my new i-phone 7 and get this message at the end:

Internal Server Error - Read

The server encountered an internal error or misconfiguration and was unable to complete your request.

Reference #3.35f90a17.1503594967.1bf3cb1e

What can I do to get the backup done?

Best regards

A. Minder