If you are trying to call the Orchestration that are exposed as webservice , You will come acros this error below . This usually happens in Dev machines where Biztalk as well as IIS is on the same machine.
The Messaging Engine failed to register the adapter for "SOAP" for the receive location "/VirtDir/App.asmx". Please verify that the receive location is valid, and that the isolated adapter runs under an account that has access to the BizTalk databases.
An attempt to connect to "BizTalkMgmtDb" SQL Server database on server "Server" failed with error: "Cannot open database requested in login 'BizTalkMgmtDb'. Login fails.".
The "SOAP" adapter is suspending an outbound message going to destination URL
1 ) This issue occurs because the App pool identity that is used by the application pool for the exposed Web service is not added as to the BizTalk Isolated Host Users group. This is needed because the message needs to get properly authenticated to get submitted.
2 ) Also this account needs permission to the %systemroot%\Temp folder on the server that exposes the Web service .This is needed as the web service (.asmx) files are JIT compiled to create DLLs in the %systemroot%\Temp folder.
Giving these correct access and permissions should solve the issue .