This article describes the cause and possible solution for a failed screenshot with the error "FATAL: No bootable medium found! System halted."
Figure 1 - Example of the error message
The virtual machine could not find an active partition, volume with valid boot information, or a valid operating system. If this is happening with the Linux agent, see the article Linux Screenshot Fails With A "No Bootable Medium" Error Message.
Verify that the volume the operating system resides on is part of the backup job. You can check this in Agent Configuration: Volume Level Backup Control.
Figure 2 shows an example of the "System Reserved" and "D:\" volumes being excluded from the backup job.
Figure 2 - Volume Level Backup Control
Verify that no other partitions are set as active (bootable) on the protected machine.
If the system has a System Reserved volume, try excluding it from future backups and deleting it in the Volume Level Backup Control options. To remove the System Reserved volume, click the Delete button under the Delete Dataset header for the System Reserved entry. After excluding and removing the System Reserved volume, take a new backup and then schedule a screenshot for the new backup.