ASP.NET

function onAddUser(e){
        var email = $get("<%= txtUserEmail.ClientID %>").value;
        var password = $get("<%= txtPassword.ClientID %>").value;
        var firstName = $get("<%= txtFirst.ClientID %>").value;
        var lastName = $get("<%= txtLast.ClientID %>").value;
        var address1 = $get("<%= txtAddress1.ClientID %>").value;
        var address2 = $get("<%= txtAddress2.ClientID %>").value;
        var city = $get("<%= txtCity.ClientID %>").value;
        var state = $get("<%= ddlState.ClientID %>").value;
        var zip = $get("<%= txtZip.ClientID %>").value;
        var parentElement = e.target.parentNode;

    PersonalWebSite1.UserService.WriteUser(email, password, firstName, lastName, address1, address2,
        city, state, zip, onWriteUserSuccess, onWriteUserFailure, parentElement);

    //Note normally returning false from the event handler code works
    //but for some reason in the latest version of FireFox it does not
    //so preventDefault is used
    e.preventDefault();
    return false;
}

<asp:FileUpload ID="MPNCPNFileUpload" runat="server" />
                   <asp:Button ID="MPNCPNFileUploadButton" runat="server" OnClick="TabFileUploadButton_Click"
                       Text="Upload" /></td></tr>
                   <tr><td><asp:CustomValidator ID="TabFileUploadErrorCustomValidator" runat="server" Display="Dynamic"
                       ErrorMessage="CustomValidator"
                       OnServerValidate="TabFileUploadedCustomValidator_ServerValidate">TextFile with MPN-CPN Details should
                       be uploaded</asp:CustomValidator>

<asp:FileUpload ID="DocumentFileUpload" runat="server" />
                    <asp:Button ID="DocumentUploadButton" runat="server" OnClick="DocumentUploadButton_Click" 
                        Text="Upload" /></td></tr>                 
                    <tr><td><asp:CustomValidator ID="DocumentUploadedCustomValidator" runat="server" Display="Dynamic"
                        ErrorMessage="CustomValidator" 
                        OnServerValidate="DocumentUploadedCustomValidator_ServerValidate">Document 
                    must be uploaded</asp:CustomValidator>

protected void TabFileUploadedCustomValidator_ServerValidate(object source, ServerValidateEventArgs args)
    {
        CustomValidator cv = (CustomValidator)source;
        args.IsValid = !String.IsNullOrEmpty(System.Convert.ToString(ViewState["PartsDetailFileName"]));
        
    }

protected void DocumentUploadedCustomValidator_ServerValidate(object source, ServerValidateEventArgs args)
    {
        CustomValidator cv = (CustomValidator)source;
        args.IsValid = !String.IsNullOrEmpty(System.Convert.ToString(ViewState["DocumentFileId"]));
    }