Error 8021: unable to validate the user or group - reported in NetBackup Console

Problem

Error 8021: unable to validate the user or group - reported in the NetBackup Administration Console.

Error Message

Error 8021: unable to validate the user or group

At debug level 1, nbatd logs report status 5 i.e. access denied  as below

[Debug] NB 51216 nbatd 18 PID:3144 TID:816 File ID:18 [No context] 1 [debugmsgs] (authntdomain.cpp:1835) CAuthNTDomain::validatePrpl - NetUserGetInfo for user test_user ,domain lab.veritas.com failed, error 5

Cause

"NetBackup Authentication" service (nbatd) is running as LSA Local System Administrator) causing the query to report an access denied failure. 

Solution

Execute the below command and test authentication:

"C:\Program Files\Veritas\NetBackup\sec\at\bin\vssat.bat" authenticate -p <user_name> -d nt:<domain_name> -b localhost:13783

If the command is successful, change the logon account for "NetBackup Authentication" service (nbatd) on the master server, to the Domain Account.