Sorry for the late response due to summer.
Here is a quick fix for that. Please open up Graph.cs and replace method CreateDefinedParameterVariables at about line #820 with the following code:
Debug.LogError(string.Format("A Parameter Variable named '{0}' was due to be created in a Global Blackboard named '{1}', which was not found in the scene. Parameter was not created.",paramName,bbName));
continue;
}
}
Debug.Log(string.Format("Creating Parameter Variable named '{0}' on Blackboard named '{1}'.",paramName,bb.name));