100091 Windows Azure Online Backup Agent: Unable to backup a file
Symptoms
Unable to backup a file.
Cause
File input/output (FILE IO) failure occurred for one of the files included in the backup.
Resolution
There was a failure in attempting to backup the file data for a particular file. This file will be included in the next scheduled backup and should be backed up at that time. You can retry the backup operation using Backup Now to see if the error recurs. If the error recurs, check the list of files included in the backup policy and verify that the files included are correctly located and accessible.