Backup attempts fail with an error indicating that the virtual machine's state was not valid during the backup process.

This issue arises due to the following reasons:

1. Offline Cluster Disk:

   The Cluster Disk containing the Virtual Machine's Virtual Hard Disk file is offline.

2. Offline Scale-out File Server Role:

   The Scale-out File Server role, in which the VM's disk is located, is offline.

3. Checkpoint Deletion Delay:

   Deletion of checkpoints for the Virtual Machine is taking an extended period.

To address this issue, consider the following solutions:

1. Cluster Disk Status:

1. Connect to the Cluster using the Failover Cluster Manager on any of the cluster nodes.
2. Navigate to "Storage" and then "Disks."
3. Locate the relevant Cluster Disk associated with the VM's Virtual Hard Disk file.
4. If the disk is offline, change its status to online.
5. Reattempt the backup job.
   

2. Scale-out File Server Role:

1. Connect to the Cluster through the Failover Cluster Manager on any cluster node.
2. Navigate to "Roles" and find the respective Scale-out File Server (SOFS) role.
   
3. If the role is offline, set it to online.
   
4. Retry the backup job
   

3. Checkpoint Deletion Progress:

1. Open Hyper-V Manager.
2. Check whether checkpoint deletion is underway for the affected Virtual Machine.
3. If checkpoint deletion is in progress, allow it to complete.
4. Once the deletion is finished, initiate the backup job again.