You will need to mark the entire vault for backup first, then use the option for the Incremental Backup.
To mark the entire vault for backup please follow these steps:
1. Click on File and go down to the Properties option.
2. When the box opens up, please click on the Backup option to the left side.
3. You will now see in blue "Mark entire media vault for backup." Please select this.
4. Another window will open stating there are a certain amount of items in your media vault, do you want to schedule them all for backup? Please click Yes and then click on OK.
5. Now when you go into your media library and select the Vault Ribbon you will be able to click on the Incremental Backup option where you have the selection to write to a hard drive now, burn CDs or DVDs later. Please select "Write to a hard drive now" and then click on the Next option.
6. Where it says select the size image you want to create, please drop this window down and select Hard Disk - No size limit.
7. Next, click on the button with the three dots to it.
8. Please browse to your external hard drive and create a new folder for your backup.
9. Once the folder is created, select it, and click on OK.
10. Now you should be able to click on the Backup option.
Find out how to recover from a manual backup by clicking here.