Create color group and color swatches with scripting error 21

[tianhanz63841248]

Hi I was hoping to create a color group that contents 128 color swatches from white to black, grey scale color. however I keep getting this error messgae 21

here is my code, please let me know if anyone can help, thank you!

// Specify the number of swatches you want to create
var numSwatches = 128;

// Create an empty array to store the swatches
var swatches = [];

// Loop through each swatch and calculate the brightness value
for (var i = 0; i < numSwatches; i++) {
var brightness = i * 1 / (numSwatches - 1);

// Create a new swatch with the brightness value
var newSwatch = new GrayColor();
newSwatch.gray = brightness;
swatches.push(newSwatch);
}

// Add the swatches to the swatches panel
for (var j = 0; j < swatches.length; j++) {
var newSpot = app.activeDocument.swatches.add(swatches[j]);
newSpot.name = "Swatch " + (j + 1);
}

// Select all the swatches
app.activeDocument.swatches["Swatch 1"].selected = true;
for (var k = 2; k <= swatches.length; k++) {
app.activeDocument.swatches["Swatch " + k].selected = true;
}

// Export the swatches as an ASE file
var aseFile = new File("~/Desktop/GrayScaleSwatches.ase");
app.activeDocument.swatches["Swatch 1"].parent.exportSelected(aseFile, ExportType.ASE);

[c.pfaffenbichler]

Where did you get this Script? 

Photoshop Documents have no swatches so how should this work? 

[c.pfaffenbichler]

Have you tried using ScriptingListener.plugin to record the process of creating a Color Swatch yet in order to wrap the AM-code in a function?