Android Ant Error: resolve to a path with no project.properties file for project

问题

I do this in an Ant Script. I link a library Project, update them and build them. But I keep getting this error in the headline. Anyone knows how to fix this?

<target name="updateProject">

    <echo>updating Project...</echo>
    <exec dir="${scannerLibrary_home}" executable="ant">
        <arg line="project"/>
        <arg line="update"/>
        <arg line="--path"/>
        <arg line="."/>
    </exec>
    <exec dir="${projectroot}" executable="ant">
        <arg line="project"/>
        <arg line="update"/>
        <arg line="--path"/>
        <arg line="."/>
    </exec>


    <exec dir="${android_home}/tools" executable="./android">
        <arg line="update"/>
        <arg line="project"/>
        <arg line="--target"/>
        <arg line="4"/>
        <arg line="--path"/>
        <arg line="${scannerLibrary_home}"/>
    </exec>
    <exec dir="${android_home}/tools"  executable="./android"> 
        <arg line="update"/>
        <arg line="project"/>
        <arg line="--target"/>
        <arg line="4"/>
        <arg line="--path"/>
        <arg line="${targetdir}"/>
    </exec>

    <antcall target="buildScanner"/>
</target>

<target name="buildScanner">
    <exec dir="${scannerLibrary_home}"  executable="ant"> 
        <arg line="debug"/>
    </exec>
    <antcall target="buildProject"/>
</target>

<target name="buildProject">
    <exec dir="${targetdir}"  executable="ant"> 
        <arg line="debug"/>
    </exec>
    <antcall target="install"/>
</target>

来源：https://stackoverflow.com/questions/12086154/android-ant-error-resolve-to-a-path-with-no-project-properties-file-for-project