You dont get it. the parentDocument is the main application where the horizontal list is loaded. here is the complete code...

"gallery.mxml"

<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml" layout="absolute" xmlns:ns1="components.*">

<mx:Script>
<![CDATA[
import mx.rpc.events.ResultEvent;
import mx.controls.Alert;
import mx.managers.CursorManager;
import mx.collections.ArrayCollection;

[Bindable]
private var dataAr1:ArrayCollection;
private function concernOriginalReceived(event:ResultEvent):void {
dataAr1 = event.result as ArrayCollection;
}

private function imageListHandler(event:Event):void{
trace("Someone clicked on the Large Green Button!");
remoteObj.gallery.send();
}

]]>
</mx:Script>

<mx:RemoteObject id="remoteObj" destination="ColdFusion" source="gallery.cfcs.gallery">
<mx:method name="gallery" result="concernOriginalReceived(event)" fault="Alert.show(event.fault.faultString,'Error');">
<mx:arguments>
<imgid_home>{imgid_home.text}</imgid_home>
</mx:arguments>
</mx:method>
</mx:RemoteObject>


<mx:Model id="homeImages">
<images>
<img1>{dataAr1.getItemAt(0).img1}</img1>
<img2>{dataAr1.getItemAt(0).img2}</img2>
<img3>{dataAr1.getItemAt(0).img3}</img3>
<img4>{dataAr1.getItemAt(0).img4}</img4>
</images>
</mx:Model>


<ns1:imageName id="home_tiles" x="0" y="140" addImageEvent="imageListHandler(event)"/>
<ns1:imgGallery x="170" y="140"/>
<mx:Text id="imgid_home" text="{home_tiles.selectedItem.imgid_home}"/>
<mx:Label id="img1" x="254" y="0" text="{dataAr1.getItemAt(0).img1}"/>
<mx:Image x="499" y="0">
<mx:source>assets/homeprofile_pics/extra_pics/{homeImages.img4}</mx:source>
</mx:Image>
</mx:Application>

"imageName.mxml"

<?xml version="1.0" encoding="utf-8"?>
<mx:List xmlns:mx="http://www.adobe.com/2006/mxml" dataProvider="{dataAr}" labelField="location" creationComplete="Init()" change="ClickEventHandler()">
<mx:Script>
<![CDATA[
import mx.rpc.events.ResultEvent;
import mx.controls.Alert;
import mx.managers.CursorManager;
import mx.collections.ArrayCollection;

public function Init():void{
homeSvc.load();
}

[Bindable]
private var dataAr:ArrayCollection = new ArrayCollection;
public function displayResult(event:ResultEvent):void{
dataAr = new ArrayCollection( (event.result as ArrayCollection).source);
}

private function ClickEventHandler():void{
trace("Ouch! I got clicked! Let me tell this to the world.");
dispatchEvent(new Event("addImageEvent", true));// bubble to parent
}
]]>
</mx:Script>

<mx:RemoteObject id="homeSvc" destination="ColdFusion" source="gallery.cfcs.homes1" showBusyCursor="true" fault="CursorManager.removeBusyCursor();Alert.show(event.fault.message)">
<mx:method name="load" result="displayResult(event)" />
</mx:RemoteObject>

<mx:Metadata>
[Event(name="addImageEvent", type="flash.events.Event")]
</mx:Metadata>
</mx:List>

"imgGallery.mxml"

<?xml version="1.0" encoding="utf-8"?>
<mx:Canvas xmlns:mx="http://www.adobe.com/2006/mxml" width="100%" height="100%">

<mx:Script>
<![CDATA[
import mx.collections.*;

[Bindable]
private var home_img1:ArrayCollection = new ArrayCollection(home_img);

]]>
</mx:Script>

<!--<mx:Array id="home_img">
<mx:Object label="img1" fullImage="assets/homeprofile_pics/extra_pics/{parentDocument.homeImages.img1}" />
<mx:Object label="img2" fullImage="assets/homeprofile_pics/extra_pics/{parentDocument.homeImages.img2}" />
<mx:Object label="img3" fullImage="assets/homeprofile_pics/extra_pics/{parentDocument.homeImages.img3}" />
<mx:Object label="img4" fullImage="assets/homeprofile_pics/extra_pics/{parentDocument.homeImages.img4}" />
</mx:Array> -->

<mx:Array id="home_img">
<mx:Object label="img1" fullImage="assets/homeprofile_pics/extra_pics/bedroom-decorations.jpg" />
<mx:Object label="img2" fullImage="assets/homeprofile_pics/extra_pics/Interior_Classical_bedroom_interior_005016_.jpg" />
<mx:Object label="img3" fullImage="assets/homeprofile_pics/extra_pics/clean-livingroom.jpg" />
<mx:Object label="img4" fullImage="assets/homeprofile_pics/extra_pics/regreen-interior-design-ideas-remodeling-green-kitchen.jpg" />
</mx:Array>

<mx:Label text="Title:" width="100%" textAlign="center" y="88" fontSize="12"/>
<mx:Text width="100%" text="Mable tiled walls, spacious kitchen with well furnished furniture" y="115" textAlign="center" fontSize="12"/>
<mx:Label x="190" y="143" id="home_id" text="{parentDocument.home_tiles.selectedItem.imgid_home}"/>

<mx:VBox width="100%" verticalGap="2" horizontalAlign="center" borderStyle="solid" cornerRadius="10" bottom="0">
<mx:HorizontalList id="photoList" dataProvider="{home_img}" labelField="label" iconField="fullImage" itemRenderer="components.Thumbnail" columnCount="4" width="98%"/>
</mx:VBox>
<!--image used to test if "parentDocument.homeImages" actually loads an image and the result was a success. it loads an image-->
<mx:Image x="348.5" y="169" source="assets/homeprofile_pics/extra_pics/{parentDocument.homeImages.img4}"/>
</mx:Canvas>

"Thumbnail.mxml"

<?xml version="1.0" encoding="utf-8"?>

<mx:VBox xmlns:mx="http://www.adobe.com/2006/mxml"
width="100" height="110"
paddingTop="0" paddingBottom="0"
verticalScrollPolicy="off" horizontalScrollPolicy="off"
verticalGap="0" horizontalAlign="center" >

<mx:Label id="position" width="100" height="20" text="{data.label}"/>

<mx:Canvas id="imageBox" width="95%" height="90" borderStyle="solid">
<mx:Image source="{data.fullImage}" width="100%" height="100%" horizontalAlign="center" verticalAlign="middle" />
</mx:Canvas>

</mx:VBox>

please any flex expert out there help me....