Problem: Our Veeam backups starting failing with an authentication issue to our Data Domain.
Solution: Upon investigation it appears the DDBoost account was locked. This appears to have been reset to 90 days after a recent upgrade.
1) SSH to Data Domain and log in as sysadmin account
2) Run following command:
user password aging show
As you see it is set to 90 days.
3) To set the DDBoost acocunt to 99999 days use following command
user password aging set DDBOOST max-days-between-change 99999