Droplist has a SelectedValue which is invalid because it does not exist in the list of items

First I would like to state that I am using a Datatable to fill my gridview and the select that I am using is a left join. here is a my select

SELECT PM.num [num], PMT.MedType [MedType], 
...Some other columns...
FROM [pharm_meds] PM 
LEFT JOIN [pharm_meds_Type] PMT ON  PM.[MedType_ID] = PMT.[num]

and I am being lazy and currently have a asp:DropDownList being filled by a sqldatasource located outside the gridview

<asp:TemplateField ItemStyle-Width = "75px"  HeaderText = "Med Type">
        <ItemTemplate>
            <asp:Label ID="lblMedType" runat="server" Text='<%# Eval("MedType")%>'></asp:Label>
        </ItemTemplate>
        <EditItemTemplate>
            <asp:DropDownList ID="ddlMedType" DataSourceID="sdsMedType" DataTextField="MedType" DataValueField="MedType" SelectedValue='<%# Bind("num") %>' Text='<%# Bind("num") %>' runat="server">

            </asp:DropDownList>
        </EditItemTemplate>  
        <FooterTemplate>               
            <asp:DropDownList ID="ddlMedType" DataSourceID="sdsMedType" DataTextField="MedType" DataValueField="MedType" SelectedValue='<%# Bind("num") %>' Text='<%# Bind("num") %>' runat="server" OnSelectedIndexChanged="ddlMedType_SelectedIndexChanged" AutoPostBack="True" >

            </asp:DropDownList>
        </FooterTemplate> 
        <ItemStyle Width="75px" />
    </asp:TemplateField>

here is the sqldatasource for the asp:DropDownList:

<asp:SqlDataSource ID="sdsMedType" runat="server" ConnectionString="<%$ ConnectionStrings:SiteSqlServer2 %>" SelectCommand="SELECT [num], [MedType] FROM [pharm_meds_Type]"></asp:SqlDataSource>

Now the trouble I have occurs when I want to edit the existing rows here is my code for it

protected void EditMedication(object sender, GridViewEditEventArgs e)
    {
        DropDownList ddlMedType = (DropDownList)gvMainView.FooterRow.FindControl("ddlMedType");
        string strMedID = ddlMedType.Text;
        using (SqlConnection con = new SqlConnection(ConfigurationManager.ConnectionStrings["SiteSqlServer2"].ConnectionString))
        {
            SqlCommand cmd1 = new SqlCommand("SELECT [num], [MedType] from [pharm_meds_Type] where [MedType] = @MedID", con);
            cmd1.Parameters.AddWithValue("@MedID", strMedID);
            con.Open();
            using (SqlDataReader reader1 = cmd1.ExecuteReader())
            {
                while (reader1.Read())
                {
                    MyMedType = reader1.GetInt32(0);
                }
                ddlMedType.SelectedValue = Convert.ToString(MyMedType); //failed attempt to fix the issue
                gvMainView.EditIndex = e.NewEditIndex;
                BindData();
            }
        }

    }

When I hit the edit link I get the error in the title. How do I fix this?