Please help, error when placedLayerEditContents.

You also need to be careful in you script when it come to  opening a smart object layer's object to edits its content.  If the layer's object  is a vector image  or a camera raw image the  object will open in application  or Plug-in that processes those images formats  AI or ACR your Photoshop Script's next statement would be executed after AI of ACR  is done the object would or would not have been updated the  object work document would not be open in Photoshop.  I use code that  r-bin posted to test the smart object and bypass vector and Raw object in my mockup scripts for Photoshop does not  have  support for vector and raw image formats.   

I have also has issues where the Object work file created in temp by Photoshop did not open in Photoshop  I had the add some code to handle the problem if/when it occured.

////// open smart object //////
function openSmartObject (theLayer) {
	current = app.activeDocument;
	if (theLayer.kind == "LayerKind.SMARTOBJECT") {
		runMenuItem(stringIDToTypeID('placedLayerEditContents'));
		if ( current == app.activeDocument) {
			try {         
				var r = new ActionReference();     
				r.putProperty(stringIDToTypeID("property"), stringIDToTypeID("smartObject"));  
				r.putIdentifier(stringIDToTypeID("layer"), theLayer.id);  
				var name = executeActionGet(r).getObjectValue(stringIDToTypeID("smartObject")).getString(stringIDToTypeID("fileReference"));         
				}  
			catch (e) { throw theLayer + " Smart Object Did not Open"; }  
			var workFile = new File(Folder.temp + "/" +  name);  // May work for both Windows and Mac
			if (workFile.exists) app.open(File(workFile));
			if ( current == app.activeDocument) throw theLayer + " Smart Object Did not Open";
		}
	}
	return app.activeDocument
};

These work for me:

var idplacedLayerEditContents = stringIDToTypeID( "placedLayerEditContents" );
    var desc3536 = new ActionDescriptor();
executeAction( idplacedLayerEditContents, desc3536, DialogModes.NO );

or

app.runMenuItem(stringIDToTypeID('placedLayerEditContents'));