Yes it is the pre-release, so if thats it, then it explains a lot I'm trying to do all the math manually now to do the burn without nodes anyway, which is apparently hard. Below is the trace for you.
python FirstOrbit.py
Calculating circular burn
Traceback (most recent call last):
File "FirstOrbit.py", line 26, in <module>
node = vessel.control.add_node(vessel.orbit.time_to_apoapsis, prograde=delta_v)
File "<string>", line 1, in <lambda>
File "C:\Python35\lib\site-packages\krpc\client.py", line 88, in _invoke
raise RPCError(response.error)
krpc.error.RPCError: 'SpaceCenter.Control_AddNode' threw an exception.
System.NullReferenceException: Object reference not set to an instance of an object
at ManeuverNode.OnGizmoUpdated (Vector3d dV, Double ut) [0x00000] in <filename unknown>:0
at KRPC.SpaceCenter.Services.Node..ctor (.Vessel vessel, Double ut, Single prograde, Single normal, Single radial) [0x00000] in <filename unknown>:0
at KRPC.SpaceCenter.Services.Control.AddNode (Double ut, Single prograde, Single normal, Single radial) [0x00000] in <filename unknown>:0
at (wrapper managed-to-native) System.Reflection.MonoMethod:InternalInvoke (object,object[],System.Exception&)
at System.Reflection.MonoMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) [0x00000] in <filename unknown>:0