How to catch file upload error?

To catch uploader error, you need to use CuteWebUI_AjaxUploader_OnTaskError or CuteWebUI_AjaxUploader_OnError event.

Example:

<%@ Page Language="C#" %>
<%@ Register TagPrefix="CuteWebUI" Namespace="CuteWebUI" Assembly="CuteWebUI.AjaxUploader" %>
<script type="text/javascript">
    function CuteWebUI_AjaxUploader_OnError(msg)
    {
         alert("global error:"+msg);
         return false;
    }
    function CuteWebUI_AjaxUploader_OnTaskError(obj,msg,reason) 
    {
        alert("file error:"+obj.FileName+" , "+msg);
        return false;
    }
</script>
<script runat="server">
      void Uploader_FileUploaded(object sender, UploaderEventArgs args)
      {
            args.MoveTo(Server.MapPath("~/Uploads/"));
      }
</script>
<html>
<head>
</head>
<body>
<form runat="server" id="theForm">
      <CuteWebUI:Uploader runat="server" ID="Uploader1" 
            InsertText="Upload File" OnFileUploaded="Uploader_FileUploaded">
      </CuteWebUI:Uploader>
</form>
</body>
</html>