vProtect backups fail with an invalid username or password error.
vProtect backups fail due to invalid ESX credentials.
Supply the appropriate ESX Administrator credentials in Settings > Clients, Networking, and Notifications > Clients for vCenter servers/ESX hosts
An ESX user account with full administrative privileges is required to perform vProtect VM backups. The user or group must have the role administrator.
For more detailed information on backup failures and performance issues see Unitrends KB 5062 - Backup Failures and Performance Issues