Resolution:
TIBCO Siebel Adapter internally uses the EAI TIBCO HTTP Agent business service. This error is generally thrown if the BS is not imported successfully. Please import the EAI TIBCO HTTP Agent business service (.sif under &ltAdapter_Home>\siebel folder).
Note: The inbound services namely Subscription and Request-Response Services would not require the EAI TIBCO HTTP Agent for their functioning. But without importing the agent, the adapter throws this error especially with TIBCO Administrator and hence importing the agent is recommended.
Please refer to TIBCO Adapter for Siebel User's Guide --> Chapter 8 Using the EAI TIBCO HTTP Agent Business Service, for more information on importing the BS