Retrospect Backup 7.7 -1101 and -3420 Cannot Read Errors

Problem: After solving a problem with Retrospect 7.7 not being able to list the Mailboxes of an Exchange 2007 server for backup ( Retrospect Backup 7.7 Will Not List Exchange 2007 Mailboxes ) I found that I was receiving -1101 and -3420 Cannot Read errors.

Solution:

I worked with Retrospect to resolve the -1101 and -3420 Cannot Read errors.
The -1101 turn out to be items that the user has deleted between the
time the backup started and when their individual mailbox back backed
up. A few of these are expected especially when you run a Full Backup
of the Exchange email system during business hours (8am to 5 pm). Retrospect
ran for 5 hours. 1st it scanned all 45G of mailbox data and then backed it up.
Between the start and the finish, some users deleted an email or calendar item
and therefore, Retrospect could not find the item.

The -3420 are corrupted items like spam messages. Out of 743,000
email messages backed up only 12 were -3402 errors and this is not unusual.
Retrospect indicates that these corrupted emails are often spam.
Confirmed with Restrospect that the Exchange Backups are completing
properly.