The input network dataset does not define a cost attribute named TruckTravelTime.
The TruckTravelTime cost attribute must be available on the input network dataset for the tools in the NetworkAnalysis and NetworkAnalysisSync geoprocessing services to run as expected. If this cost attribute is missing, the tools use the first cost attribute defined on the network dataset, which may cause unexpected analysis results.
If your network dataset can model the travel time taken by trucks to travel on streets, define a cost attribute named TruckTravelTime on the network dataset. Otherwise, do not use the Truck Time option when specifying the Impedance parameter on the tools.