Unable to use services

Hi - I'm having a problem trying to use services in a process.

I have some processes that were built for us by a contractor that use a web service to make a call to an Oracle database.  When I try to click on this call in the Process Designer I get the error "Failed to load/render Property Editor".

I also get the same error if I try to drag a new Invoke Web Service node onto the designer.

Does anyone know how I might be able to fix this?

Thanks

Dan