Backup of a Hyper-V virtual machine fails with the following error:
Failed to obtain associated virtual system settings
One of the network adapters of the VM is not connected to a virtual switch.
Acronis Backup products cannot back up virtual machines where one or more network adapters are not connected to a virtual switch. This is current product design.
Find the affected virtual machine: it can be found in the Activity details, after a line Failed to back up virtual machine...
Connect the virtual machine adapter to a virtual switch using Hyper-V manager. If the virtual machine has several adapters, make sure that they are all connected or remove the disconnected adapters.
After connecting all adapters, you can later set some of them to "Not connected" if needed - Acronis Backup requires <Connection> element in virtual machine configuration file, constant connection is not obligatory.