I have the following markup:

<ext:Store ID="storePagos" runat="server">
        <Reader>
            <ext:JsonReader ReaderID="IdCursoConcepto">
                <Fields>
                    <ext:RecordField Name="IdCursoConcepto" />
                    <ext:RecordField Name="IdcConcepto" />
                    <ext:RecordField Name="Concepto" />
                    <ext:RecordField Name="Monto" />
                    <ext:RecordField Name="Activo" Type="Boolean" />
                </Fields>
            </ext:JsonReader>
        </Reader>
    </ext:Store>

<ext:GridPanel ID="gridPagos" runat="server" StoreID="storePagos" Height="150" StripeRows="true"
    Title="Conceptos configurados" Width="400px" ClicksToEdit="1">
    <ColumnModel>
        <Columns>
            <ext:Column DataIndex="IdCursoConcepto" Hidden="true" ColumnID="IdCursoConcepto">
            </ext:Column>
            <ext:Column DataIndex="IdcConcepto" Hidden="true" ColumnID="IdConcepto">
            </ext:Column>
            <ext:Column DataIndex="Concepto" Header="Concepto" ColumnID="Concepto" Width="200px">
            </ext:Column>
            <ext:Column DataIndex="Monto" Header="Monto" ColumnID="Monto" Width="70px">
                <Editor>
                    <ext:NumberField ID="nfMontoGrid" runat="server">
                    </ext:NumberField>
                </Editor>
            </ext:Column>
            <ext:CheckColumn DataIndex="Activo" Header="Activo" ColumnID="Activo" Width="70px"
                Editable="true">
            </ext:CheckColumn>
        </Columns>
    </ColumnModel>
    <SelectionModel>
        <ext:RowSelectionModel SingleSelect="true">
        </ext:RowSelectionModel>
    </SelectionModel>
</ext:GridPanel>
And am having problems when I trie to add records manually with this code:

private void CargarTablaPagos(params object[] valores)
        {
            if (valores != null &amp;&amp; valores.GetLength(0) > 0)
            {
                IDictionary<string, string> registro = new Dictionary<string, string>();
                registro.Add("IdCursoConcepto", valores[0].ToString());
                registro.Add("IdcConcepto", valores[1].ToString());
                registro.Add("Concepto", valores[2].ToString());
                registro.Add("Monto", valores[3].ToString());
                registro.Add("Activo", valores[4].ToString());


                storePagos.AddRecord(registro);
                storePagos.CommitChanges();
            }
        }
The problem is no matter wath value I put in "Activo" (true or false), in the gridPanel the checkbox is always checked. How can I solve this issue?

Thanks in advance for the help.