What error do you get when you try to backup?
You can of course also try and move all configuration files and disks manually to the new node, and then, on the new node, add a storage pointing to where you put the disks with the same name as the original storage (so the configuration files are still correct). If the new cluster already has VMs with the same ID's you'll need to rename the configs and disks and edit the configs to reference the renamed disks.