How to change the <globalization> to en-gb

I have also tried:

http://forums.daypilot.org/Topic.aspx/583/changing_culture_from_enus_in_sqldemo_breaks_update

The 3 pieces of code tht influence this are the following:

Web.config file -- <globalization uiCulture="en-GB" culture="en-GB"/>

Default.aspx.cs --

protected void EventDetail_ItemUpdating(object sender, DetailsViewUpdateEventArgs e)
{
e.NewValues["eventstart"] = Convert.ToDateTime(e.NewValues["eventstart"], new CultureInfo("en-GB"));
e.NewValues["eventend"] = Convert.ToDateTime(e.NewValues["eventend"], new CultureInfo("en-GB"));
}

Default.aspx --

<asp:DetailsView ID="EventDetail" runat="server" DefaultMode="Edit" OnItemUpdated="EventDetail_ItemUpdated"
DataSourceID="SqlDataSourceDetail" DataKeyNames="id"
AutoGenerateEditButton="True" OnItemCommand="EventDetail_ItemCommand"
Width="50px" AutoGenerateInsertButton="True" AutoGenerateRows="False" OnItemInserted="EventDetail_ItemInserted"
CssClass="detail" GridLines="None" OnItemUpdating="EventDetail_ItemUpdating">

The error i get is when i try and book an event is -- arithmitic overflow error converting expression to data type datetime.

I still cannot figure out what I am doing wrong...

Is there any namespaces i need to include ??

Using ...;

my problem has something to do with the item_updating event or the modalpopup extender. When i run the application it shows the weekends as the last 2 days and monday as the first day. My problem is when i try and book a room it goes to a grey screen and shows a white box.