looking at the backup log, it looks like vss had issues during the backup.
Can i have you re-run the backup?
If you still get the same error, Open the backup set, go to set properties, Disaster recovery /Image restore options and then choose the option for incremental \ Differential backup, and below that, choose full backup. What this will do is have UltraBac use its own driver instead of Volume shadow copy.
Test Engineer / Beta Manager