Problem with Details View

[GaryDevenay]

Hey,
I am trying to insert data to a database via the inserting fuction in the details view but i seem to get this error

You tried to assign the Null value to a variable that is not a Variant data type.

this is my code for the details view

        <asp:DetailsView ID="DetailsView1" runat="server" Height="50px" Width="348px" 
            AllowPaging="True" AutoGenerateRows="False" CssClass="input" 
            DataKeyNames="REG No,121" DataSourceID="AccessDataSource1">
            <Fields>
                <asp:BoundField DataField="MAKE" HeaderText="Make" SortExpression="MAKE" />
                <asp:BoundField DataField="MODEL" HeaderText="Model" SortExpression="MODEL" />
                <asp:BoundField DataField="COLOUR" HeaderText="Colour" 
                    SortExpression="COLOUR" />
                <asp:BoundField DataField="REG No" HeaderText="Reg Number" ReadOnly="True" 
                    SortExpression="REG No" />
                <asp:BoundField DataField="D O R" HeaderText="Date of Registration" SortExpression="D O R" />
                <asp:BoundField DataField="PRICE" HeaderText="Price" SortExpression="PRICE" />
                <asp:BoundField DataField="MILEAGE" HeaderText="Mileage" 
                    SortExpression="MILEAGE" />
                <asp:BoundField DataField="PICTURE" HeaderText="Picture" 
                    SortExpression="PICTURE" />
                <asp:BoundField DataField="121" HeaderText="ID Number" InsertVisible="False" 
                    ReadOnly="True" SortExpression="121" />
                <asp:CommandField ShowEditButton="True" ShowInsertButton="True" />
            </Fields>
        </asp:DetailsView>

<asp:AccessDataSource ID="AccessDataSource1" runat="server" 
            DataFile="~/App_Data/Datastore.mdb" 
            DeleteCommand="DELETE FROM STOCKLIST" 
            InsertCommand="INSERT INTO STOCKLIST([121], [REG No], COLOUR, MODEL, MAKE, [D O R], PRICE, MILEAGE, PICTURE) VALUES (@ID,@Reg_No,@Colour,@Model,@Make,@D_O_R,@Price,@Mileage,@Picture)" 
            SelectCommand="SELECT MAKE, MODEL, COLOUR, [REG No], [D O R], PRICE, MILEAGE, PICTURE, [121] FROM STOCKLIST" 
            
            UpdateCommand="UPDATE STOCKLIST SET [121] = @ID, MAKE = @Make, MODEL = @Model, COLOUR = @Colour, [REG No] = @Reg_No, [D O R] = @D_O_R, PRICE = @Price, MILEAGE = @Mileage, PICTURE = @Picture">
            <InsertParameters>
                <asp:Parameter Name="@ID" />
                <asp:Parameter Name="@Make" />
                <asp:Parameter Name="@Model" />
                <asp:Parameter Name="@Colour" />
                <asp:Parameter Name="@Reg_No" />
                <asp:Parameter Name="@D_O_R" />
                <asp:Parameter Name="@Price" />
                <asp:Parameter Name="@Mileage" />
                <asp:Parameter Name="@Picture" />
            </InsertParameters>
        </asp:AccessDataSource>

[GaryDevenay]

Does anyone know how this can be fixed or even where my problem is?

[GaryDevenay]

I think it could possibly be the parameters but I am not sure what is actually wrong with them!