ddlimp utility - Unable to connect to the database.

ddlimp utility failed to connect to database with correct connection details.

ddlimp /U SIEBEL /P ***** /C siebel /G SSE_ROLE /F D:\OBIEE11G\Oracle_BI1\biapps\dwrep\Upgrade\CTLFiles\DDL_OLTP.CTL /L D:\OBIEE11G\Oracle_BI1\biapps\
dwrep\Upgrade\CTLFiles\DDL_OLTP.log

Connecting to the database...
Unable to connect to the database...

Fix:-
Create a USER DSN instead of SYSTEM DSN with the same connection details and use the DSN in ddlimp utility parameters.