Can't resolve IVY

My ANT build.xml starts like this

<?xml version="1.0" encoding="UTF-8"?>
<project name="myProject" default="clean_dist" xmlns:ivy="antlib:org.apache.ivy.ant">

    <!--
    ===================================================================
    Initialization target
    ===================================================================
    -->
    <target name="init">
        <property name="javac.target" value="1.5"/>
        <property name="javac.source" value="1.5"/>
        <property name="name" value="myProject"/>
        <!-- retreive dependencies with ivy -->
        <ivy:settings file="./ivysettings.xml">
            <credentials host="10.100.27.27:9100"  realm="Repository archiva" username="user" passwd="passwd" />
        </ivy:settings>
        <ivy:retrieve/>
    </target>

xmlns:ivy="antlib:org.apache.ivy.ant"
<ivy:settings file="./ivysettings.xml">
and <ivy:retrieve/>
are all highlighted in red

I can run the targets successfully if I put the ivy.jar in the IDEA ant lib directory C:\Program Files\JetBrains\IntelliJ IDEA 9779\lib\ant\lib\
So why are the ivy parts still highlighted in red?