Getting "Failed to open tool" message when trying to run geoprocessing tool from C# code

I've been experimenting with the Military Aspects of Terrain Template, which has a toolbox associated with it. I've been using the following WPF Runtime code, which should open a tool in the associated toolbox . . .

private void RunToolButton_Click(object sender, RoutedEventArgs e)
{
        ESRI.ArcGIS.RuntimeManager.Bind(ESRI.ArcGIS.ProductCode.Desktop);
        //Set a reference to the IGPCommandHelper interface.
        IGPToolCommandHelper pToolHelper = new GPToolCommandHelperClass() as IGPToolCommandHelper;


        //Set the tool you want to invoke.
        string toolboxName = @"C:\ArcGISForDefense\Intelligence\MilitaryAspectsOfTerrainTemplate\Maps\Toolbox\Military Aspects of Terrain Toolbox.tbx";
        pToolHelper.SetToolByName(toolboxName, "CoverFromFlatTrajectoryWeapons");

        // Generate the array of parameters.
        IArray parameters = new ArrayClass();
        parameters.Add(@"C:\ArcGISForDefense\Intelligence\MilitaryAspectsOfTerrainTemplate\Maps\OperationGDB.gdb\BrigadeAOI");
        parameters.Add(@"C:\ArcGISForDefense\Intelligence\Operational_Environment\Data\MAoT\MAoT.gdb\CombinedVegetationCoverage");
        parameters.Add(@"C:\ArcGISForDefense\Intelligence\MilitaryAspectsOfTerrainTemplate\Maps\OperationGDB.gdb\CoverAreas");


        //Invoke the tool. 
        pToolHelper.Invoke(parameters);
}

When I try to run the code, I get the following error message, then it crashes at the "invoke" method . . . "Failed to open tool CoverFromFlatTrajectoryWeapons (Military Aspects of Terrain Toolbox.tbx)" Am I using the right syntax for opening a tool that is in the "Cover and Concealment" toolset, which is in the "Military Aspects of Terrain Toolbox.tbx" toolbox? Am I doing anything wrong that would prompt this error message? I would appreciate any help.

I also wrote the following routine as an alternative, but this also bombs when it gets to the last line of the routine . . .

 public void Run_CoverFromFlatTrajectoryWeapons_Tool()
    {
        // Initialize the geoprocessor.
        //Insert this line before invoking any ArcObjects to bind Engine runtime. 

        ESRI.ArcGIS.RuntimeManager.Bind(ESRI.ArcGIS.ProductCode.Engine);
        GeoProcessor gp = new GeoProcessor();

        // Add the toolbox.
        gp.AddToolbox(@"C:\ArcGISForDefense\Intelligence\MilitaryAspectsOfTerrainTemplate\Maps\Toolbox\Military Aspects of Terrain Toolbox.tbx");           

        // Generate the array of parameters.
        IVariantArray parameters = new VarArrayClass();
        parameters.Add(@"C:\ArcGISForDefense\Intelligence\MilitaryAspectsOfTerrainTemplate\Maps\OperationGDB.gdb\BrigadeAOI");
        parameters.Add(@"C:\ArcGISForDefense\Intelligence\Operational_Environment\Data\MAoT\MAoT.gdb\CombinedVegetationCoverage");

        parameters.Add(@"C:\ArcGISForDefense\Intelligence\MilitaryAspectsOfTerrainTemplate\Maps\OperationGDB.gdb\CoverAreas");
        // Execute the model tool by name.
        gp.Execute("CoverFromFlatTrajectoryWeapons", parameters, null);
    }

By the way, the above mentioned tool does run well with the specified parameters when running it in ArcMap.

Thanks, Renee