The error pops-up after providing the username and password when attempting to create an "E-mail Messages" backup set to protect Exchange 2013 using the EWS option.
1. The domain name instead of the Exchange Server IP address is used when creating the backup set.
2. permissions not propagated to Exchange after implementing the prerequisites for EWS backup sets.
1. Use the IP address of the backup source Exchange Server when creating the set.
2. reboot the backup target Exchange computer.