Oracle Backup fails with 0xe0001403 login account could not be authenticated

I am not able to run a succesful Oracle backup.

The log file on the Oracle Server from BEUTility looks as if the ORACLE-part runs fine (message logon succesful), but something else goes wrong.

Whatever I do , the jobs end with error 0xe0001403.

The message text asks me to update logon credentials on "the list of authentication resources" on the BE Server (sorry, my system is in german).

The only point I can think of is "Login accounts administration"

Can someone give me a hint?

EDIT: Oracle Server and Backup Exec Server are in a Workgroup "PRAXIS" - not a Windows Domain