API Call failed with message: A general system error occurred: Protocol error from VMX (91861)

In vRanger’s Failed Tasks the job Logs (tab at the bottom) shows that the backup failed with “API Call failed with message: A general system error occurred: Protocol error from VMX” right after it tried to take a quiesced snapshot.

On the Virtual Center it fails with the same error when you take a quiesced snapshot manually.

The cause is the Volume Shadow Copy service

1. Log into the Virtual Machine experiencing the error
2. Restart the Volume Shadow Copy service
3. Restart VMware Tools service
4. As a test please take a quiesced snapshot via the vSphere client
5. If you were able to take a quesced snapshot be sure to Delete all from Snapshot Manager
6. Run the backup job as usual