I spent most of my morning troubleshooting an orchestration that I exposed as an ASMX Web Service. I created the WS as one-way, or fire and forget as I wanted to test out truly asynchronous SOAP message handling.
During testing the WS call, IIS responed prompty with a 202 Accepted message, but BTS showed no trace of the message. Not only had the message not been written to the MessageBox, there was no indication whatsoever that a message had even been received.
After going nuts, reconfiguring the Host Instnance security credentials (I even went so far as to spin up a new local account for this purpose), I came across a post in which a fellow frustrated developer was reciting a checklist of all of the things he had already checked. Among the items were "Ensure that the ASP.NET process account is a member of BizTalk Isolated Host Users."
VIOLA! That was it. Because I am running Windows XP, the ASP.NET worker process runs under ASPNET. In Windows 2003, this is NETWORK SERVICE.
Lesson learned...