When troubleshooting calls made via the BizTalk SOAP adapter I often find myself wanting to check the data that was posted to the web service. Adding the following to a test asmx page does the trick:
HttpContext.Current.Request.SaveAs("D:\\log_folder\Request_" + Guid.NewGuid().ToString() + ".txt", true);
Don't forget to grant access to the log_folder for the id that the web service runs under.