This warning can occur if you are using an older version of NI VLM. Please first make sure that you have the newest version of VLM installed on your PC. The latest version can be downloaded from the following page: Volume License Manager download page
If you already have the most up-to-date version, then you can also try to choose a different saving direction for your backup file. It's a good way to isolate if the issue is happening because of the folder you selected or because of NI VLM.
If the issue still persists after changing the directory, then this issue is most likely happening because there's some kind of corruption in your Volume License Manager. Please try repairing NI VLM from the NI Package manager. Here are the steps on how to repair a non-working or corrupted software: Repair Software In NI Package Manager (NIPM)