When making a modification to a VMware VM’s settings, you get this error:
Cannot complete operation due to concurrent modification by another operation.
You get this error because another operation is modifying the VM you are trying to modify. In other words, another user or process (some sort of virtual machine management software?) is making a modification to the VM at the same time that you are.
VMware will also tell you that it cannot complete the operation due to concurrent modification if the client is running slowly and you press the OK or Apply button twice when modifying VM settings.