Customized script to open/edit linked files is not working as expected

Ok. So here is the simplified (well, as simple as possible) example. Open the "Overview.indd" and run the script on that file. Which should open the "Product" files and change layer visibility on placed files therein.

Right now apparently it only creates an error when there's a difference. So you need to uncheck something in the Dialog.

And here's the script, thanks for any help!

// object containing the layers we have in the different kinds of files.
var layertypes = {
    techinfo: [
      {name: "Container", showDefault: true},
      {name: "Information", showDefault: true}
      ],
    layout: [
      {name: "Badge", showDefault: true},
      {name: "Artwork", showDefault: true}
      ]
};

// stores the desired visibility.
var checklist = {
    techinfo: [],
    layout: []
    };

var doc,
    settings;

// Collection for the "Product" files we want to open.
var products = [];

var thisLink,
    thisFile,
    thisFileName,
    thisDoc,
    thisDocLinks;

var currentLink, 
    currentLinkname,
    currentLayer,
    currentChecklistItem;

var ft,
    layer;

Main();

function Main() {
  if(app.documents.length == 0){
    alert("No documents are open. Please open a document and try again.");
    exit();
  }
  else {
    doc = app.activeDocument;
    settings = saveSettings();
    app.linkingPreferences.checkLinksAtOpen = false;

    myDialog();

    restoreSettings(settings);
  }
}

// Dialog gets constructe from the layertypes object.
function myDialog() {
  var myDialog = app.dialogs.add({name:"Show / Hide Layers", canCancel: true});
  with(myDialog) {
    with(dialogColumns.add()) {
      with(dialogRows.add()) {
        staticTexts.add({ staticLabel: "Techinfo" });
        for (var i = 0; i < layertypes.techinfo.length; i++) {
          with(dialogRows.add())
            checklist.techinfo.push(checkboxControls.add({ 
              staticLabel: layertypes.techinfo[i].name, 
              checkedState: layertypes.techinfo[i].showDefault 
            }));
        }
      }
    }
    with(dialogColumns.add()) {
      with(dialogRows.add()) {
        staticTexts.add({ staticLabel: "Layout" });
        for (var i = 0; i < layertypes.layout.length; i++) {
          with(dialogRows.add())
            checklist.layout.push(checkboxControls.add({ 
              staticLabel: layertypes.layout[i].name, 
              checkedState: layertypes.layout[i].showDefault 
            }));
        }
      }
    }
  }
  if (myDialog.show() == true) {

    checkLinks(doc.links);
    
    if(products.length > 0) {
      changeNestedLayers(products);
    }

    alert("Done!");
  } else {
    myDialog.destroy();
  }
}

// The problematic function.
function changeNestedLayers(linksArr) {
  for (l = linksArr.length - 1; l >= 0; l--) {

    thisLink = linksArr[l];
    thisFile = File(thisLink.filePath);
    thisFileFullPath = thisFile.fullName;

    thisDoc = app.open(thisFile, true);
    $.writeln("Opened: " + thisFile);


    thisDocLinks = thisDoc.links;

    for(var s = thisDocLinks.length - 1; s >= 0; s--) {
      currentLink = thisDocLinks[s];
      currentLinkname = currentLink.parent.itemLink.name;

      if (currentLink.parent.constructor.name == "ImportedPage" && currentLink.parent.itemLink != null && currentLink.parent.itemLink.linkType == "InDesign Format Name") {

        if(hasSubstring(currentLinkname, "Techinfo")) {
          changeLayerVisibility(currentLink, "Techinfo");
        }
        if(hasSubstring(currentLinkname, "Layout")) {
          changeLayerVisibility(currentLink, "Layout");
        }

      }
    }

    if (thisDoc.converted) {
      thisDoc.save(File(thisFileFullPath))
    } else {
      thisDoc.save()
    }    
    $.writeln("Closing: " + thisDoc.fullName);
    thisDoc.close(SaveOptions.NO);

    if (thisLink.status == LinkStatus.LINK_OUT_OF_DATE) {
      thisLink.update();
    }
  }
}

// the other problematic function.
function changeLayerVisibility(thisLink, filetype) {
  ft = filetype.toLowerCase();
  for (var k = 0; k < layertypes[ft].length; k++) {
    layer = thisLink.parent.graphicLayerOptions.graphicLayers.item(layertypes[ft][k].name);
    if (layer.isValid) {
      $.writeln(layer.currentVisibility);
      $.writeln(checklist[ft][k].checkedState);
      // If the following line is commented out, all goes well.
      // Otherwise error, pointing to line 149. File already open...
      layer.currentVisibility = checklist[ft][k].checkedState;
    }
  }
}

// check and change layer visibility for direct links (Not in use right now).
// push products to separate list for opening (in use).
function checkLinks(linksArr) {
  for (var l = 0; l < linksArr.length; l++) {

    var thisLink = linksArr[l];
    var linkname = thisLink.parent.itemLink.name;

    if (thisLink.parent.constructor.name == "ImportedPage" && thisLink.parent.itemLink != null && thisLink.parent.itemLink.linkType == "InDesign Format Name") {

      if(hasSubstring(linkname, "Product")) {
        products.push(thisLink);
      } 
      else if(hasSubstring(linkname, "Techinfo")) {
        changeLayerVisibility(thisLink, "Techinfo");
      } 
      else if(hasSubstring(linkname, "Layout")) {
        changeLayerVisibility(thisLink, "Layout");
      } 
    }
  }
}

// Utility Functions
function hasSubstring(string, substring) {
  if(string.indexOf(substring) !== -1) return true;
}

function saveSettings() {
  var settingsTemp = {
    checkLinksAtOpen: app.linkingPreferences.checkLinksAtOpen
  };
  return settingsTemp;
}

function restoreSettings(settings) {
  app.linkingPreferences.checkLinksAtOpen = settings.checkLinksAtOpen;
  app.scriptPreferences.userInteractionLevel = UserInteractionLevels.INTERACT_WITH_ALL;
}