I was trying to setup HTTPRequestResponse sample from BizTalk SDK samples
2 errors that I got after setting it up are
1. error 401 not authorized
2. error 404 not found
Fixes to these are
1. Run Application pool under user who is part of BizTalk User Groups
2. Add BTSHTTPReceive.dll to Web Services Extensions in IIS; set access to 'allow'. Web Services Extensions can from configured in IIS . ASP.net uses ISAPI to communicate with biztalk we need to enable it over here. By default Windows 2003 prohibits ISAPI applications. Adding BTSHTTPReceive.dll to this list we are saying that allow ISAPI for this dll
Cheers
Vishy