GameParseException: Missing property definition for option ''maxConstructionsPerType'' in attachment ''unitAttachment''

Here is my code

    <attachment name="unitAttachment" attachTo="fort" javaClass="games.strategy.triplea.attachments.UnitAttachment" type="unitType">
      <option name="defense" value="2"/>
      <option name="createsResourcesList" value="-1:PUs"/>
      <option name="hitPoints" value="2"/>
      <option name="isAAforCombatOnly" value="true"/>
      <option name="targetsAA" value="infantry:cavalry"/>
      <option name="maxRoundsAA" value="3"/>
      <option name="requiresUnits" value="infantry"/>
      <option name="isConstruction" value="true"/>
      <option name="constructionType" value="fort"/>
      <option name="constructionsPerTerrPerTypePerTurn" value="1"/>
      <option name="maxConstructionsPerType" value="5"/>
    </attachment>

I want to limit the building of forts to 1 per turn, up to a max of 5 per territory.

Is there something wrong with my code.