Resolution:
The value for the input argument “AgentHTTPServer” should be specified with the name of machine where the adapter is running with the port number. Please try using full name or the IP address of the machine instead of merely specifying the name (an2131028).

In addition, confirm if you have imported correct EAI TIBCO HTTP Agent Business Service based on the Siebel application you have at your end. You may like to refer to Chapter 9 of Siebel adapter documentation for more information and steps to import the BS.