Transport Codes in OSB

Question

hi, i am getting this

<tran:response-code  xmlns:tran="http://www.bea.com/wli/sb/transports"&gt;2&lt;/tran:response-code&gt;&lt;tran:response-message  xmlns:tran="http://www.bea.com/wli/sb/transports"&gt;Internal Server Error</tran:response-message><tran:encoding  xmlns:tran="http://www.bea.com/wli/sb/transports"&gt;utf-8&lt;/tran:encoding&gt;&lt;http:http-response-code&gt;500&lt;/http:http-response-code&gt; 

What does the transport response code 2 mean? I have seen many others as well, Can someone tell me what they mean?