Hi Nash,
Ensure that:
1. The ECC username used is a System(Background) user with RFC execution privillege.
2. You have entered proper parameters in the System Connection Editor.
3. You have entered exact case password in credential editor.
4. Test connection with a JCo Interface by calling BAPI_TRANSACTION_COMMIT as simple.
If still the issue persists, refer the below thread.
http://scn.sap.com/message/6034694
Regards,
Prashant