Oracle Instance - Validation Failed

Hi,

Currently trying to register an oracle instance from within the NetBackup Administration Console.

Using OS credentials and have also inputted my Oracle Authentication details.

I select 'OK' and the validation fails with "Validation of operating system user/password failed for client".

I understand this error message relates to incorrect credentials but I have confirmed they are correct on the target client, and the same credentials are running the oracle application.

Would anyone have any suggestions in order to help me troubleshoot this issue?

Thanks in advance.