vProtect backups fail with an invalid username or password error.
vProtect backups fail due to invalid ESX credentials.
On UI, navigate to Configure > Protected Assets section > select the vCenter/esxi host > Edit > Enter the updated/correct credentials for vCenter servers/ESX hosts > Save
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