PROBLEM
While restoring a VM to a VMware host, the VM restores successfully, but you receive the warning 'One or more network adapters could not be added to the VM' as shown below:
CAUSE
This warning is caused when a VM has a virtual Ethernet card that connects to a distributed virtual switch port of type 'DistributedVirtualSwitchPortConnection'
More information here: http://pubs.vmware.com/vsphere-60/index.jsp?topic=%2Fcom.vmware.wssdk.apiref.doc%2Fvim.vm.device.VirtualEthernetCard.DistributedVirtualPortBackingInfo.html
SOLUTION
In this case the restore is still a fully successful one, however it will leave out the Virtual NIC. You will simply need to create the Virtual NIC manually from vSphere after the VM Backup Restore completes.