Hi Tux,
Can you create a page by the code below and let your client test it? Does it get the same issue?
<%@ Page Language="C#" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head id="Head1" runat="server">
<title>example</title>
</head>
<body>
<form id="form1" runat="server">
<CuteWebUI:Uploader ID="Uploader1" runat="server">
</CuteWebUI:Uploader>
</form>
</body>
</html>
And let him disable the Anti-virus and firewall to test it too.
Regards,
Ken