Hi, there is really ugly bug:
1) Create new SOAP-UI project
2) Import WSDL, check create simulation service
3) Save project
4) Rename interface <-- THIS IS IMPORTANT
5) Try WS mock service, everything should work well
6) Save and close project
7) Open project, everything looks good, but WSDL Operation property of service mock is missing.
Now your mocked service is broken -you will get NPE, you are unable to open mock response.
If you open soapui xml project file, you can see the cause - con:mockOperation@interface contains old interface name.
After you manual rewrite interface name to new value you will repair the project.