Hello Abhijeet,
The error is related to your portal configuration, try to check supplier pre-selection directly from Service Internet Frameworks (SICF transaction) and you will be able to run the transaction..
To solve the problem, you Portal consultant must create the system alias to your SUS-ROS system to allow Portal Role to be linked to the proper ABAP system during the call in your Portal JAVA stack.
Also, check and complete correctly the SLD names in the BBP_BACKEND_DEST table.
Regards,
SG