I have an instance of WebUpload control that I need to configure to fire the Upload events on the server side, but I still want to trap when the user selects files with the wrong extension on the client side.

In my ascx file, I have coded

        <igjq:WebUpload ID="igUpload1"
            runat="server"
            OnUploadFinishing="igUpload1_OnUploadFinishing"
            OnUploadFinished="igUpload1_OnUploadFinished"
            OnUploadStarting="igUpload1_OnUploadStarting"> 
            <ClientEvents OnError="showAlert" />
        </igjq:WebUpload>

In the code behind (CS) file, I have

$.ig.loader(function () {
    $("#igUpload1").igUpload({
        mode: 'multiple',
        multipleFiles: true,
        maxUploadedFiles: 5,
        maxSimultaneousFilesUploads: 1,
        allowedExtensions: ["txt", "doc", "png"],
        progressUrl: "Services/IGUploadStatusHandler.ashx",
        controlId: "serverID1",
        iguploadonerror: function (e, args) {
            showAlert(e, args);
        },
        onError: function (e, args) {
            showAlert(e, args);
        }
    )};
)};

When I code the OnUploadStarting to cancel the event with a server message, the onError event does fire and I can display the message there.  This is good.

However, when I test the client side by selecting a file with a bad extension, neither error event fires.

What do I need to change to trap the OnError event on the client?