I've exposed quite a lot of my orchestrations as web services; while doing that I faced numerous problems sojust thought of summarizing all possible resolutions techniques here
1. SOAP Port not created
2. All properties required for correlation are not promoted; so uninstall assembly are redeploy it
3. SOAP Port created is not bound to orchestration
4. Web service is using anonymous access; remove this anonymous access; keep only windows authentication
5. User account for web service application pool doesn't have access to %temp% folder
6. User account for web service application pool is not member of IIS_WPG group
7. Client to this web service is sending credentials
8. Do iisreset once to ensure all changes are reflected
9. User account for Isolated host has enough rights to access SQL server
10. If you are using Http and SOAP adapters both then create seperate instances of isolated hosts for them
11. Changing receive location pipeline to XML receive pipeline from default passthru pipeline
12. Finally check event log for more information
Cheers
Vishy