When you try to modify a protection group that contains Hyper-V Virtual Machine (VM) guests or you try to remove a VM from a protection group, you receive an error message that resembles the following:

Removing Guest_Name failed:
Error 157: Guest_Name cannot be added to protection because it is already a member of a protection group.


This issue is due to duplicate entries in the DPM database. The duplicate entries may occur after a protected virtual machine is migrated from one Hyper-V cluster to a different Hyper-V cluster and then that VM is re-protected on the new cluster.


To fix this issue, contact Microsoft Support for help removing the duplicate entries. To prevent future occurrences, enable live migration. To do this, see Set up protection for live migration.


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