Hi John,
A few remarks:
- SOAP vs REST API - if you haven't decided yet, I'd recommend to choose REST API. SOAP API is quite limited in scope (mostly related to workflow execution), while REST covers much more areas. Also, SOAP API will not be developed further; for example, it won't be extended to support SSO.
- Perspectives plug-in - it is for vCO 4.x only and is not supported in vCO 5.x and newer
- Stack trace shows that the exception is happening in Multi-node plug-in. Which build/version do you have installed?