Mapguide - add gridfiles to transformation

[fieldguy]

This is cross posted from the Map Developer forum.  I know I shouldn't do that but answers are rare there.

I am trying to simulate the manual process of adding grid files to coordinate transformation definitions (MAPCSLIBRARY - Edit). The code below generates a "System is Protected" error and I can't figure out why - or how to solve this.

Here's the contents of the post.

I want to add the Canada NTV2_0.gsb file to the built in NAD27_to_NAD83 transformation definition.  I am getting a "system is protected" error.  I think part of the problem is the collection I am trying to pass.  I have the gsb file in the folder but it is not assigned to the transformation yet. 

I am trying to automate the manual process (MAPCSLIBRARY - Edit).  According to the MapGuide documentation "NewGridFile Creates a new, empty MgCoordinateSystemGeodeticTransformGridFile object that can be added to the collection set via SetGridFiles".  That is the part I can't figure out. 

The error occurs on defparams.SetGridFiles(newgridfiles);  Below it is commented out - remove the comments for the error msg.

[CommandMethod("modtrans")]
        public void modtrans()
        {
            Autodesk.AutoCAD.ApplicationServices.Document doc = Autodesk.AutoCAD.ApplicationServices.Core.Application.DocumentManager.MdiActiveDocument;
            Editor ed = doc.Editor;
            string msg = "modtrans";
            //
            MgCoordinateSystemFactory csysfactory = new MgCoordinateSystemFactory();
            MgCoordinateSystemCatalog csyscatalog = csysfactory.GetCatalog();
            MgCoordinateSystemGeodeticTransformDefDictionary transformsdict = csyscatalog.GetGeodeticTransformDefDictionary();
            MgCoordinateSystemEnum transformsenum = transformsdict.GetEnum();
            MgStringCollection transformnames = transformsenum.NextName(transformsdict.GetSize());
            for (int i = 0; i < transformsdict.GetSize(); i++)
            {
                MgCoordinateSystemGeodeticTransformDef transformdef = transformsdict.GetGeodeticTransformationDef(transformnames.GetItem(i));
                if (transformdef.GetTransformName().ToString() == "NAD27_to_NAD83")
                {
                    MgCoordinateSystemGeodeticInterpolationTransformDefParams defparams = transformdef.GetParameters() 
                        as MgCoordinateSystemGeodeticInterpolationTransformDefParams;
                    MgDisposableCollection gridfilelist = defparams.GetGridFiles();
                    MgDisposableCollection newgridfiles = new MgDisposableCollection();
                    if (gridfilelist.GetCount() > 0)
                    {
                        msg += "\noriginal gridfile count " + gridfilelist.GetCount();
                        for (int j = 0; j < gridfilelist.GetCount(); j++)
                        {
                            MgCoordinateSystemGeodeticTransformGridFile gridfile = 
                                (MgCoordinateSystemGeodeticTransformGridFile)gridfilelist.GetItem(j);
                            msg += "\ngrid file " + gridfile.GetFileName();
                            newgridfiles.Add(gridfile);
                        }// for int j
                    }// if gridfile count > 0
                    // this is what I am trying to do 
                    // from the MapGuide API Reference I am using
                    // virtual MgCoordinateSystemGeodeticTransformGridFile* MgCoordinateSystemGeodeticInterpolationTransformDefParams::NewGridFile
                    // () [pure virtual]
                    // Creates a new, empty MgCoordinateSystemGeodeticTransformGridFile object that can be added to the collection set via SetGridFiles.
                    // Returns:
                    // Returns a new, unitialized MgCoordinateSystemGeodeticTransformGridFile instance The caller is resonsible for disposing
                    // the object if no longer needed.
                    MgCoordinateSystemGeodeticTransformGridFile addgsbfile = defparams.NewGridFile();
                    string gsbdestination = "C:\\ProgramData\\Autodesk\\Geospatial Coordinate Systems 14.00\\Canada";
                    string gridfilename = gsbdestination + "\\ntv2_0.gsb";
                    addgsbfile.SetFileName(gridfilename);
                    addgsbfile.SetFileFormat(2);                // ntv2 
                    newgridfiles.Add(addgsbfile);
                    msg += "\nnew gridfile count " + newgridfiles.GetCount();
                    // this generates a "The coordinate system initialization failed. The system is protected" error 
                    // defparams.SetGridFiles(newgridfiles);
                }// if its the transformation to change
            }// for int i
            ed.WriteMessage(msg);
        }// modtrans