Make sure your IP is directly on the MGMT port on both vlt members and destinations are reversed, and of course your cable between them tests good and is at least 18 inches.

Switch A

vlt-domain 1
backup destination 10.0.0.2

interface mgmt1/1/1
description "VLT Backup"
no shutdown
ip address 10.0.0.1/24

Switch B

vlt-domain 1
backup destination 10.0.0.1

interface mgmt1/1/1
description "VLT Backup"
no shutdown
ip address 10.0.0.2/24