I finally got the scheduled task toy run successfully by applying the permissions listed below. The really weird thing is that the DiRT backup would run successfully if performed manually under the old permissions but not as a scheduled task.
You will need to run the Disaster Recovery Backup tool logged in as an account that has administration rights to SQL and, if you've selected to backup messages, an account that has Exchange Service account rights. This is much trickier than it sounds and will not be the case for any account you may have used to install Unity since it would have been a member of the Domain Admins group which is explicitly denied this right in Exchange. Please see the Configuring Permissions for DiRT section for details on how to go about this. Once you've launched the application, you need only use the “Browse†button to indicate where you want the backup files written and hit the “backup†button. The progress is indicated by the checkboxes next to each task as it's undertaken.
Also, I believe you've mentioned you are using the Two-Hop Method. Please review below and let me know that you are providing local space with more then enough room for the backup.
Using The Two Hop Backup
The actual backup of the SQL data for the main Unity database and, optionally, the reports database is done using the SQL services themselves. As such the permissions to write files to the target directory are limited by the account the SQL services are running under. If your site is using the local system account for these services then writing the SQL backup data to an off box location will fail. Further, you are using a domain account for the SQL services but don't want to grant read/write permissions to the off box location then the SQL backup portion will fail as well.
This is a fairly common scenario so we provided a simple mechanism to work around it. First do the SQL backup to a local drive the move the backed up database files to the off box target using the account DiRT backup is running under and then delete the local copies of the backup files. This is called the “two hop†method.
You can use this method by checking the “Use 'two hop' method for backing up SQL data†check box and then providing a local target to use. Be sure to use a local drive where you have room enough to do the backup. For large systems the SQL tables can be large so be sure to leave yourself plenty of room.
