XPage - Problem with number validator in Combo Box Control

I’m developing a XPage with a label and combo box. I set up the combo a few number values for choices and set the converter as xp:converterNumber with type “number”.But, when I tried to submit, I got a errors display controler informing "Validation Error: Value is not valid ".

The following is the source of the XPage:

<?xml version="1.0" encoding="utf-8"?>

<xp:view xmlns:xp=“http://www.ibm.com/xsp/core”>

xp:panel

<xp:table>

  <xp:tr>

    <xp:td colspan="2">

      <xp:messages id="messages1"></xp:messages>

    </xp:td>

  </xp:tr>

  <xp:tr>

    <xp:td>

      <xp:label value="Periodicidade" id="label1"></xp:label>

    </xp:td>

    <xp:td>

      <xp:comboBox id="comboBox1"

      value="#{requestScope.periodicidade}">

        <xp:this.converter>

          <xp:convertNumber type="number" integerOnly="true">

          </xp:convertNumber>

        </xp:this.converter>

        <xp:selectItem itemLabel="1" itemValue="1">

        </xp:selectItem>

        <xp:selectItem itemLabel="2" itemValue="2">

        </xp:selectItem>

        <xp:selectItem itemLabel="3" itemValue="3">

        </xp:selectItem>

        <xp:selectItem itemLabel="4" itemValue="4">

        </xp:selectItem>

        <xp:selectItem itemLabel="5" itemValue="5">

        </xp:selectItem>

        <xp:selectItem itemLabel="6" itemValue="6">

        </xp:selectItem>

        <xp:selectItem itemLabel="12" itemValue="12">

        </xp:selectItem>

        <xp:selectItem itemLabel="18" itemValue="18">

        </xp:selectItem>

        <xp:selectItem itemLabel="24" itemValue="24">

        </xp:selectItem>

        <xp:selectItem itemLabel="36" itemValue="36">

        </xp:selectItem>

      </xp:comboBox>

    </xp:td>

  </xp:tr>

</xp:table>

<xp:button value="Enviar" id="button1">

  <xp:eventHandler event="onclick" submit="true"

  refreshMode="complete">

    <xp:this.action>

      <![CDATA[#{javascript:var docPer:NotesDocument = database.createDocument();

docPer.replaceItemValue(“Form”,“fo_associacaoPadrao”);

docPer.replaceItemValue(“ca_assPeriodicidade”, requestScope.periodicidade);

docPer.replaceItemValue(“ca_assPadraoCodigo”, sessionScope.padraoCodigo);

docPer.replaceItemValue(“ca_assPadraoTitulo”, sessionScope.padraoTitulo);

docPer.save();

context.redirectToPage(“main”)}]]>

</xp:this.action>

  </xp:eventHandler>

</xp:button>

<xp:button value="Cancelar" id="button2">

  <xp:eventHandler event="onclick" submit="true"

  refreshMode="complete" immediate="true" save="false">

  </xp:eventHandler>

</xp:button>

</xp:panel>

xp:this.navigationRules

<xp:navigationRule outcome="xsp-success" viewId="/main.xsp">

</xp:navigationRule>

</xp:this.navigationRules>

</xp:view>

I dont understand why this is happening since I use alias on choices of the combo box.

Any help will be welcome.