mailbox backup fails

Mailbox-level backup - is a type of backup that stores contents of Exchange mailboxes and/or public folders.

Acronis Backup accesses the contents using Messaging Application Programming Interface (MAPI), so backing up multiple mailboxes may take a long time.  Backing up at a mailbox level makes sense when you need to frequently back up a small number of mailboxes. Otherwise, consider a database-level backup (Information Store backup).

Symptoms

After installing security update for Exchange Server, Exchange mailbox backups fail with the following error:

Cannot open public folder or mailbox. 
Access is denied