Why has moving GridView code to an ascx given an "Databinding expressions are only supported on objects that have a DataBinding event" exception?

I created a GridView in code with a DataTable as its data source which worked fine. I have now moved the GridView creation into a .ascx file to make it easier to format.

For some reason this has started triggering the HttpParseException:

Databinding expressions are only supported on objects that have a DataBinding event. System.Web.UI.WebControls.HyperLinkField does not have a DataBinding event.

What's changed to cause this difference and how do I fix it?

Original code:

// Set up columns for datagrid
var boundField = new HyperLinkField
                    {
                        HeaderText = "Title",
                        DataTextField = MembershipCollection.WebTitleColumnName,
                        DataNavigateUrlFields = new[] { MembershipCollection.WebUrlColumnName },
                        DataNavigateUrlFormatString = "{0}"
                    };

// Set up datagrid
_sitesList = new GridView
                {
                    AutoGenerateColumns = false,
                    AllowPaging = true,
                    PageSize = PageSize,
                    EmptyDataText = "No results",
                    Width = new Unit(100, UnitType.Percentage),
                    CellPadding = 2,
                    PagerSettings =
                        {
                            Visible = true,
                            Mode = PagerButtons.NextPrevious,
                            Position = PagerPosition.Bot开发者_高级运维tom,
                            NextPageText = "Next >",
                            PreviousPageText = "< Previous"
                        }
                };
_sitesList.PagerStyle.HorizontalAlign = HorizontalAlign.Center;
_sitesList.RowDataBound += GridView_RowDataBound;
_sitesList.PageIndexChanging += GridView_PageIndexChanging;
_sitesList.Columns.Add(boundField);

.ascx code:

<asp:ObjectDataSource ID="_sitesDataSource" runat="server"
    SelectMethod="GetSites"
    TypeName="System.Data.DataTable" />
<asp:GridView ID="_sitesGridView" runat="server"
    AutoGenerateColumns="false"
    AllowPaging="true"
    PageSize="<%# this.PageSize %>"
    EmptyDataText="No results"
    width="100%"
    DataSourceID="_sitesDataSource"
    OnRowDataBound="GridView_RowDataBound"
    OnPageIndexChanging="GridView_PageIndexChanging">
    <PagerSettings Visible="true" Mode="NextPrevious" Position="Bottom" NextPageText="Next >" PreviousPageText="< Previous" />
    <PagerStyle HorizontalAlign="Center" />
    <Columns>
        <asp:HyperlinkField
            HeaderText="Title"
            DataTextField="<%# MembershipCollection.WebTitleColumnName %>"
            DataNavigateUrlFields="<%# MembershipCollection.WebUrlColumnName %>"
            DataNavigateUrlFormatString="{0}" />
    </Columns>
</asp:GridView>

I just realised - I used <%# when it should have been <%= in the HyperlinkField declaration.

<%# is going to try and data bind, and as the exception indicates there is no associated data binding for the HyperlinkField. However <%= will simply execute code (i.e. insert the text from a constant).