Problems with RemoteObject and security sandbox errors

Question

I'm having trouble with an AS3 AMF RemoteObject request that is hosted on Google App Engine. I have a crossdomain.xml file in the root of the domain, and also one at the remoting endpoint.
Here are the contents of the root crossdomain.xml:
<?xml version="1.0"?>
<cross-domain-policy>
<site-control permitted-cross-domain-policies ="all"/>
<allow-access-from domain="*.appspot.com"/>
<allow-access-from domain="*.{appid}.appspot.com"/>
<allow-access-from domain="*.{appid}.com"/>
<allow-access-from domain="*.{appid}.org"/>
</cross-domain-policy>
I have replaced my application's ID with {appid}. In the endpoint crossdomain.xml, it says the exact same thing, except it omits the <site-control> tag.
Loading the swf file and testing it on my machine works just fine... I think that may have something to do with me having the debugger version of Flash Player. When I push it up to App Engine to make it public, other clients access it and get a Client.Error.MessageSend Channel.Security.Error error Error #2048 url: http://05-alpha.latest.{appid}.appspot.com/_rpc/data.
I am using Flex 4 beta, and the App Engine Python runtime. I have tried full wildcard in the crossdomain, and even accessing the data endpoint at a relative URL so as to avoid this error.
Someone please help! Thanks in advance.

Answer 1

The error happens regardless of where I access it (the beta URL, the production URL, etc).
That's literally all the actionscript code for the remote object... I've included an extended snippet below, but I have no idea why the SWF would be trying to access localhost.
Even on my development machines (where it seems to work), there's nothing running on the host/port combo it's trying to access.
Extended AS3:
FatCatStage.mxml:
<s:RemoteObject id="dataService" showBusyCursor="false" destination="data" endpoint="/_rpc/data" />
main.mxml:
<fx:Script>
<![CDATA[
               fatCatStage.dataService.RetrieveFirstGraph.addEventListener( ResultEvent.RESULT, fatCatStage.graphInitialize );
fatCatStage.dataService.RetrieveFirstGraph();
public function doGraphChange(event:ResultEvent):void
if(event.result.result!='failure')
var GraphData:Object = event.result.response;
this.lastGraphData = GraphData;
fatCatViz.removeAll()
var root:GenericSprite = fatCatViz.addNodeElement(GraphData.object,null,this.center,GraphData.object.key);
for each ( var Connection:Object in GraphData.object.connections )
this._recursiveGraph(root, Connection, center, 3);
else
Alert.show('There was an internal graphing error. Please try again.');
fatCatViz.updateInternalStructure();
this.intervalSet = setInterval(timedReLayout,500);
]]>
</fx:Script>
That's all of the relevant actionscript for the entire application. Where is it referencing localhost?