Upload file: response Text returns undefined value in IE browser

Hello everybody,

At this moment, I am encountering an issue I have not found the way to solve yet. Please give me a clue if

you can. Many thanks in advance!

I am developing a module allowing users to upload image file to server with CodeIgniter and YUI. There

are some restrictions for this upload: image files only, .GIF, JPG, ... and the maximum capacity for the

uploaded file not exceed 1 Megabyte.  And the following is my JS code:

function uploadPhoto()
{

    setGlobalMessage("");
    var sURL = _APBMRootURL + "adminMembers_controller/uploadPhoto";

    var callback =
    {
        upload: handleUploadPhotoUpload,
        failure: handleUploadPhotoFailure
    };

    var f = document.getElementById("frm_Main");
    var postData = YAHOO.util.Connect.setForm(f, true);
    var request = YAHOO.util.Connect.asyncRequest('POST', sURL, callback);

}

function handleUploadPhotoUpload(o)
{
    //alert(o.reponseText);
    if (o.responseText == undefined || o.responseText == null)
    {
        setGlobalMessage("Connection timeout. Please try again later.");
        ///setGlobalMessage("The size for the uploaded image should not exceed 1Mbs.");
        return;
    }
    ...
}

function handleUploadPhotoFailure(o)
{
    .....
}

In IE, I got o.responseText with undefined value whenever I upload the file with the capacity larger than the

 allowed maximum capacity as I mentioned above.

While I do not get this issue in Firefox.

Many thanks for your assistance!

Best Regards,

Nhat