LINQ inserting not working once deployed

 This has got me puzzled.
I'm using a DetailsView Control with the following LinqDataSource to insert new records.
All works fine on my development PC but things fail on deployment.
<asp:LinqDataSource ID="LinqDataSource_INSERT" runat="server"
        ContextTypeName="myDataContext" EnableInsert="True"
        TableName="Product_Classes" Where="companyID == @companyID">
        <WhereParameters>
            <asp:ControlParameter ControlID="DropDownList1" DefaultValue="0"
                Name="companyID" PropertyName="SelectedValue" Type="Int32" />
   &nb ...