This article describes the cause and possible solution for the screenshot verification error "BOOTMGR is compressed."
This is caused because NTFS compression has been enabled on the volume containing the Windows boot files.
When this option is selected, Windows will try to compress all files, including critical boot files.
1. On the production machine, open Windows Explorer (explorer.exe)
2. Right click the drive where BOOTMGR is located (typically C:), and select Properties.
3. Uncheck the Compress this drive to save disk space option.
5. If the "BOOTMGR is missing" message appears after a new backup, manually force a differential merge for the agent.
Note: This will force the agent to traverse the entirety of each volume being backed up, and it will appear to be a full backup. However, a diff-merge backup will only incur a cost of space on the storage array equal to a normal incremental and a minor amount of overhead.