AIR File size limit?

After tackling some other things, this has come back up on my plate.

Now I think I understand the openAsync() progress methodology, but I'm confused on how to tear off a chunk of the file to send it over the wire.

Here's my attempt to load the file via async.

public function loadAsync():void

{

     // create FileStream in read mode

          fileStream = new FileStream();

     //add listeners for the operations;

     fileStream.addEventListener(ProgressEvent.PROGRESS, AsyncProgressHandler);

     fileStream.addEventListener(IOErrorEvent.IO_ERROR, AsyncFileIOErrorHandler);

     fileStream.addEventListener(Event.COMPLETE, AsyncCompleteHandler);

     fileStream.readAhead=10485760;

     fileStream.openAsync( file, FileMode.READ);

}

private function AsyncProgressHandler(pEvent:ProgressEvent):void {

     var byteAry:ByteArray;

     fileStream.readBytes(byteAry, 0, fileStream.bytesAvailable);

          if (pEvent.bytesLoaded == file.size)

          {

               uploadBytes(byteAry);

          } else if (  pEvent.bytesLoaded == fileStream.readAhead) {

               uploadBytes(byteAry);

          }

}

Whenever I start the upload it says "Parameter bytes must be non-null