Screenshot Verification failure: BOOTMGR is missing
Issue 
This article describes the cause, and possible solutions for the screenshot verification errors:
BOOTMGR is missing
<file> is missing or corrupt
Environment 
- Datto SIRIS
- Datto ALTO
Cause 
These errors can have multiple causes, including issues with the health of the protected machine and an issue with changes not being properly captured by the backup after an update to the system.
Resolution 
Force a differential merge backup to reconcile the current backup with a new full scan of the target machine.
Running a differential merge forces the agent to check the entirety of each volume being backed up. A differential merge takes as long to run as a full backup, but only uses the storage space of a normal incremental backup.

