SonicWall virtual firewall error "This serial number is already used with another installation"

After virtual firewall is reinstalled, it needs to be registered. Sometimes registration gets error:

This serial number is already used with another installation (E1004)

The previous installation of virtual firewall was not properly removed.Customer's can de-register it in two ways:

De-Register from Firewall GUI

1. Navigate to Manage|Updates|Licenses.
2. Click DEREGISTER.
   

Delete and Register the product in MYSonicWall account (Similar to De-register)

1. To Delete the product, please follow How to Delete a Device from mysonicwall.
2. To Register the product, please follow How can I Register a Product in mysonicwall.