The error message "Unable to get previous VM snapshot" occurs due to the absence of a previous snapshot for a VM's replica in the DR site. Several scenarios can lead to this issue:

1. Deletion of the respective replica's snapshot manually in error.
2. Manual consolidation of snapshots of the replica.
3. Snapshot taken during replication, but acknowledgement for snapshot creation not communicated to BDRShield Backup agent.
   

To address this situation, follow these steps:

1. Full Replication Scheduling:

Since incremental replication for the specific VM is not feasible in this context, schedule a full replication by adhering to the steps outlined below.

   a. Multi-VM Configuration:

1. Modify the replication job that includes the problematic VM, excluding it from the replication configuration.
2. Configure the problematic VM separately for full replication in a distinct schedule.
   

   b. Single VM Configuration:

1. Temporarily suspend replication activities for the relevant replication job.
2. Reconfigure the source VM for replication to the target, using a different suffix name.
   

Note: This solution is provided to address the issue of being unable to retrieve the previous VM snapshot in BDRShield. By carefully following the prescribed steps, users can rectify the problem and ensure the continuation of the replication process for the affected VMs.