I have made paste of a my function where I create NA in 10.1. There are part of code that you don't need so you remove and try it or compare with your code
private static void CreateNetworkDataset(IFeatureDataset featureDataset, string pathAGSOutput, string pathLogEvaluator)
{
IDENetworkDataset2 deNetworkDataset = new DENetworkDatasetClass();
deNetworkDataset.Buildable = true;
deNetworkDataset.NetworkType = esriNetworkDatasetType.esriNDTGeodatabase;
IGeoDataset geoDataset = (IGeoDataset)featureDataset;
IDEGeoDataset deGeoDataset = (IDEGeoDataset)deNetworkDataset;
deGeoDataset.Extent = geoDataset.Extent;
deGeoDataset.SpatialReference = geoDataset.SpatialReference;
IDataElement dataElement = (IDataElement)deNetworkDataset;
dataElement.Name = "NetworkBusStop_ND";
deNetworkDataset.ElevationModel = esriNetworkElevationModel.esriNEMNone;
IArray sourceArray = new ArrayClass();
IEdgeFeatureSource edgeFeatureSourceStopToStop = new EdgeFeatureSourceClass();
INetworkSource networkSourceStopToStop = (INetworkSource)edgeFeatureSourceStopToStop;
networkSourceStopToStop.Name = "StopToStop";
networkSourceStopToStop.ElementType = esriNetworkElementType.esriNETEdge;
edgeFeatureSourceStopToStop.UsesSubtypes = false;
edgeFeatureSourceStopToStop.ClassConnectivityPolicy = esriNetworkEdgeConnectivityPolicy.esriNECPEndVertex;
edgeFeatureSourceStopToStop.ClassConnectivityGroup = 3;
sourceArray.Add(networkSourceStopToStop);
IEdgeFeatureSource edgeFeatureSourceConnectorsStopsStreets = new EdgeFeatureSourceClass();
INetworkSource networkSourceConnectorsStopsStreets = (INetworkSource)edgeFeatureSourceConnectorsStopsStreets;
networkSourceConnectorsStopsStreets.Name = "ConnectorsStopsStreets";
networkSourceConnectorsStopsStreets.ElementType = esriNetworkElementType.esriNETEdge;
edgeFeatureSourceConnectorsStopsStreets.UsesSubtypes = false;
edgeFeatureSourceConnectorsStopsStreets.ClassConnectivityPolicy = esriNetworkEdgeConnectivityPolicy.esriNECPEndVertex;
edgeFeatureSourceConnectorsStopsStreets.ClassConnectivityGroup = 2;
sourceArray.Add(networkSourceConnectorsStopsStreets);
IEdgeFeatureSource edgeFeatureSourceStreets = new EdgeFeatureSourceClass();
INetworkSource networkSourceStreets = (INetworkSource)edgeFeatureSourceStreets;
networkSourceStreets.Name = "Streets";
networkSourceStreets.ElementType = esriNetworkElementType.esriNETEdge;
edgeFeatureSourceStreets.UsesSubtypes = false;
edgeFeatureSourceStreets.ClassConnectivityPolicy = esriNetworkEdgeConnectivityPolicy.esriNECPEndVertex;
edgeFeatureSourceStreets.ClassConnectivityGroup = 1;
sourceArray.Add(networkSourceStreets);
IJunctionFeatureSource junctionFeatureSourceStopBus = new JunctionFeatureSourceClass();
INetworkSource networkSourceStopBus = (INetworkSource)junctionFeatureSourceStopBus;
networkSourceStopBus.Name = "StopBus";
networkSourceStopBus.ElementType = esriNetworkElementType.esriNETJunction;
junctionFeatureSourceStopBus.UsesSubtypes = false;
junctionFeatureSourceStopBus.RemoveAllClassConnectivityGroups();
junctionFeatureSourceStopBus.AddClassConnectivityGroup(2);
junctionFeatureSourceStopBus.AddClassConnectivityGroup(3);
junctionFeatureSourceStopBus.ClassConnectivityPolicy = esriNetworkJunctionConnectivityPolicy.esriNJCPHonor;
sourceArray.Add(networkSourceStopBus);
IJunctionFeatureSource junctionFeatureSourceStopsSnappedStreets = new JunctionFeatureSourceClass();
INetworkSource networkSourceStopsSnappedStreets = (INetworkSource)junctionFeatureSourceStopsSnappedStreets;
networkSourceStopsSnappedStreets.Name = "StopsSnappedStreets";
networkSourceStopsSnappedStreets.ElementType = esriNetworkElementType.esriNETJunction;
junctionFeatureSourceStopsSnappedStreets.UsesSubtypes = false;
junctionFeatureSourceStopsSnappedStreets.RemoveAllClassConnectivityGroups();
junctionFeatureSourceStopsSnappedStreets.AddClassConnectivityGroup(1);
junctionFeatureSourceStopsSnappedStreets.AddClassConnectivityGroup(2);
junctionFeatureSourceStopsSnappedStreets.ClassConnectivityPolicy = esriNetworkJunctionConnectivityPolicy.esriNJCPOverride;
sourceArray.Add(networkSourceStopsSnappedStreets);
deNetworkDataset.SupportsTurns = false;
deNetworkDataset.Sources = sourceArray;
//cost attribute
IEvaluatedNetworkAttribute evaluatedNetworkAttributeSeconds = new EvaluatedNetworkAttributeClass();
INetworkAttribute2 networkAttributeSeconds = (INetworkAttribute2)evaluatedNetworkAttributeSeconds;
networkAttributeSeconds.Name = "Seconds";
networkAttributeSeconds.UsageType = esriNetworkAttributeUsageType.esriNAUTCost;
networkAttributeSeconds.DataType = esriNetworkAttributeDataType.esriNADTDouble;
networkAttributeSeconds.Units = esriNetworkAttributeUnits.esriNAUSeconds;
networkAttributeSeconds.UseByDefault = true;
DepartureTimeEvaluator.DepartureTimeEvaluator departureTimeEvaluator = new DepartureTimeEvaluator.DepartureTimeEvaluator();
IPropertySet propertySet = new PropertySet();
propertySet.SetProperty(DepartureTimeEvaluator.DepartureTimeEvaluator.PathArcGisServerOutput, pathAGSOutput);
propertySet.SetProperty(DepartureTimeEvaluator.DepartureTimeEvaluator.PathLog, pathLogEvaluator);
departureTimeEvaluator.Data = propertySet;
INetworkConstantEvaluator netConstantAgainstDigitizedEvaluator = new NetworkConstantEvaluatorClass();
netConstantAgainstDigitizedEvaluator.ConstantValue = -1;
evaluatedNetworkAttributeSeconds.set_Evaluator(networkSourceStopToStop, esriNetworkEdgeDirection.esriNEDAlongDigitized, departureTimeEvaluator);
evaluatedNetworkAttributeSeconds.set_Evaluator(networkSourceStopToStop, esriNetworkEdgeDirection.esriNEDAgainstDigitized, (INetworkEvaluator)netConstantAgainstDigitizedEvaluator);
evaluatedNetworkAttributeSeconds.set_Evaluator(networkSourceConnectorsStopsStreets, esriNetworkEdgeDirection.esriNEDAlongDigitized, departureTimeEvaluator);
evaluatedNetworkAttributeSeconds.set_Evaluator(networkSourceConnectorsStopsStreets, esriNetworkEdgeDirection.esriNEDAgainstDigitized, departureTimeEvaluator);
evaluatedNetworkAttributeSeconds.set_Evaluator(networkSourceStreets, esriNetworkEdgeDirection.esriNEDAlongDigitized, departureTimeEvaluator);
evaluatedNetworkAttributeSeconds.set_Evaluator(networkSourceStreets, esriNetworkEdgeDirection.esriNEDAgainstDigitized, departureTimeEvaluator);
INetworkConstantEvaluator netConstantEvaluator = new NetworkConstantEvaluatorClass();
netConstantEvaluator.ConstantValue = 0;
INetworkEvaluator netConstantEvaluatorZero = netConstantEvaluator as INetworkEvaluator;
evaluatedNetworkAttributeSeconds.set_DefaultEvaluator(esriNetworkElementType.esriNETEdge, netConstantEvaluatorZero);
evaluatedNetworkAttributeSeconds.set_DefaultEvaluator(esriNetworkElementType.esriNETJunction, netConstantEvaluatorZero);
INetworkAttributeParameter2 networkAttributeParameterUseDates = new NetworkAttributeParameterClass();
networkAttributeParameterUseDates.Name = "Use Dates";
networkAttributeParameterUseDates.ParameterUsageType = esriNetworkAttributeParameterUsageType.esriNAPUTGeneral;
networkAttributeParameterUseDates.DefaultValue = false;
networkAttributeParameterUseDates.VarType = 11; // bool
INetworkAttributeParameter2 networkAttributeParameterPedestrianSpeed = new NetworkAttributeParameterClass();
networkAttributeParameterPedestrianSpeed.Name = "Pedestrian speed";
networkAttributeParameterPedestrianSpeed.ParameterUsageType = esriNetworkAttributeParameterUsageType.esriNAPUTGeneral;
networkAttributeParameterPedestrianSpeed.DefaultValue = 4.86; // Km/h
networkAttributeParameterPedestrianSpeed.VarType = 5; //double
IArray parameterArray = new ArrayClass();
parameterArray.Add(networkAttributeParameterUseDates);
parameterArray.Add(networkAttributeParameterPedestrianSpeed);
networkAttributeSeconds.Parameters = parameterArray;
IArray attributeArray = new ArrayClass();
attributeArray.Add(evaluatedNetworkAttributeSeconds);
deNetworkDataset.Attributes = attributeArray;
IFeatureDatasetExtensionContainer featureDatasetExtensionContainer = (IFeatureDatasetExtensionContainer)featureDataset;
IFeatureDatasetExtension featureDatasetExtension = featureDatasetExtensionContainer.FindExtension(esriDatasetType.esriDTNetworkDataset);
IDatasetContainer3 datasetContainer2 = (IDatasetContainer3)featureDatasetExtension;
IDEDataset deDataset = (IDEDataset)deNetworkDataset;
INetworkDataset2 networkDataset = (INetworkDataset2)datasetContainer2.CreateDataset(deDataset);
System.Console.WriteLine("Build network dataset");
INetworkBuild networkBuild = (INetworkBuild)networkDataset;
networkBuild.BuildNetwork(geoDataset.Extent);
}