Backup fails immediately with "Failed to create backup index". Logs of the backup indicate a backup failure almost immediately after the job is submitted.
Job Messages:
Job Message 2015/03/11 13:14:02 2795 Data Plugin MAILDB1 Plugin: 'Exchange Server APM', Version: '5.0.12' (Build May 16 2014 12:12:30)
Job Message 2015/03/11 13:14:03 2795 Data Plugin MAILDB1 Preparing a VSS Full Backup, mode Normal
Information 2015/03/11 13:14:09 2795 Data Plugin MAILDB1 Got the list of servers in Database Availability Group 'hqdag'
Job Message 2015/03/11 13:14:17 2795 Data Plugin MAILDB1 Got the list of databases on server 'MAILDB1'
Job Message 2015/03/11 13:14:25 2795 Data Plugin MAILDB1 Got the list of databases on server 'MAILDB2'
Job Message 2015/03/11 13:14:25 2795 Data Plugin MAILDB1 Backup selection tree successfully parsed
Error 2015/03/11 13:14:25 2795 Data Plugin MAILDB1 Failed to create backup index
Error 2015/03/11 13:14:25 2795 Jobs HQBKUP Fatal error: Backup failed
Error 2015/03/11 13:14:25 2795 Jobs HQBKUP Job Status: Backup Failed