ho provato il tuo codice (copia-incolla) e va benissimo

L'ho provato con vs2010 in una paginetta.
codice:
    <form id="form1" runat="server">
        <asp:Chart ID="CategorieChart" runat="server">
            <series>
            <asp:Series Legend="Legend1" Name="CategorieSerie" YValueType="Int32" ChartType="Column" IsValueShownAsLabel="True" ChartArea="AreaCategorie">
            <Points>
        
            <asp:DataPoint Color="Red" AxisLabel="Lunedì" YValues="2500" ToolTip="Esempio"/>
            <asp:DataPoint Color="Orange" AxisLabel="Martedì" YValues="1500"/>
            <asp:DataPoint Color="Olive" AxisLabel="Mercoledì" YValues="900"/>
            <asp:DataPoint AxisLabel="Giovedì" YValues="1212"/>
            <asp:DataPoint AxisLabel="Venerdì" YValues="441"/>
            <asp:DataPoint AxisLabel="Sabato" YValues="5555"/>
            <asp:DataPoint AxisLabel="Domenica" YValues="1987"/>
            </Points>
            </asp:Series>
            </series>
            <chartareas>
                <asp:ChartArea Name="AreaCategorie" BackColor="#ffe6c0">
                    <Area3DStyle LightStyle="Simplistic" Enable3D="true"/>
                </asp:ChartArea>
            </chartareas>    
        </asp:Chart>
    </form>
codice:
    Protected Sub Page_Load(sender As Object, e As System.EventArgs) Handles Me.Load
        Dim SerieCategorie As System.Web.UI.DataVisualization.Charting.Series = CategorieChart.Series("CategorieSerie")
        SerieCategorie.Points.AddXY("Informatica", 5)
        SerieCategorie.Points.AddXY("Filosofia", 1)
        SerieCategorie.Points.AddXY("Poesia", 4)
    End Sub