[Solved] Increase width of jQuery UI Modal Popup Box (Window)

Here I have created sample that will help you out.

HTML

<div>
    <script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.8.3/jquery.min.js"></script>
    <script src="http://ajax.aspnetcdn.com/ajax/jquery.ui/1.8.23/jquery-ui.min.js" type="text/javascript"></script>
    <link href="http://ajax.aspnetcdn.com/ajax/jquery.ui/1.8.9/themes/Blitzer/jquery-ui.css"
        rel="stylesheet" type="text/css" />
    <script type="text/javascript">
        function WebForm_OnSubmit() {
            if (typeof (ValidatorOnSubmit) == "function" && ValidatorOnSubmit() == false) {
                $("#validation_dialog").dialog({
                    title: "Validation Error!",
                    modal: true,
                    width: 500,
                    resizable: false,
                    buttons: {
                        Close: function () {
                            $(this).dialog('close');
                        }
                    }
                });
                return false;
            }
            return true;
        }
    </script>
    Name:
    <asp:TextBox ID="txtName" runat="server"></asp:TextBox>
    <asp:RequiredFieldValidator ID="RequiredFieldValidator1" Display="None" ControlToValidate="txtName"
        runat="server" ErrorMessage="Name is required."></asp:RequiredFieldValidator>
    <br />
    Email:
    <asp:TextBox ID="txtEmail" runat="server"></asp:TextBox>
    <asp:RequiredFieldValidator ID="RequiredFieldValidator2" Display="None" ControlToValidate="txtEmail"
        runat="server" ErrorMessage="Email is required."></asp:RequiredFieldValidator>
    <br />
    <br />
    <asp:Button ID="Button1" runat="server" Text="Submit" />
    <div id="validation_dialog" style="display: none">
        <asp:ValidationSummary ID="ValidationSummary1" runat="server" />
    </div>
</div>

Screenshot