I've been working through the tutorials for K2 blackpearl with rather mixed fortunes so far.  I'm trying to finish the "Building a SharePoint Integrated Workflow" one but coming up against an error.

SharePoint shows the Workflow as "Failed on Start (retrying)".

K2 Workspace's Management Console -> Workflow Server -> Process -> Instances shows "No connection could be made because the target machine actively refused it", as does Workflow Server -> Error Profiles -> All.

 The Application Event Log says:

pSharePointIntegrationServices:SetWFIntegrationDataFields], System.Xml.XmlException: Root element is missing.
   at System.Xml.XmlTextReaderImpl.Throw(Exception e)
   at System.Xml.XmlTextReaderImpl.ThrowWithoutLineInfo(String res)
   at System.Xml.XmlTextReaderImpl.ParseDocumentContent()
   at System.Xml.XmlTextReaderImpl.Read()
   at System.Xml.XmlLoader.Load(XmlDocument doc, XmlReader reader, Boolean preserveWhitespace)
   at System.Xml.XmlDocument.Load(XmlReader reader)
   at System.Xml.XmlDocument.LoadXml(String xml)
   at SourceCode.Workflow.RuntimeServices.Functions.SharePointServiceFunctions.UpdateProcessInstance(ProcessInstance processInstance, String SPIntData)

 I've no idea what's causing this. It seems that the error message in the management console is a generic TCP error.  The problem is I've no idea what service/port is trying to be connected to.  The blackpearl server is running.  Any ideas? Help would be most appreciated.