Ошибка при запуске sbt install-emulator

Я слежу за видео на этой странице http://zegoggl.es/2009/12/building-android-apps-in-scala-with -sbt.html , которые используют SBT для создания проекта Android. Однако я дохожу до попытки установить эмулятор, используя

sbt install-emulator

, и получаю следующую ошибку:

    [info] Nothing to compile.
    [info]   Post-analysis: 1 classes.
    [info] == tests / compile ==
    [info]
    [info] == awesomepad / proguard ==
    ProGuard, version 4.4
    ProGuard is released under the GNU General Public License. The authors of all
    programs or plugins that link to it (sbt, ...) therefore
    must ensure that these programs carry the GNU General Public License as well.
    Reading program directory [C:\Projects\Scala\sbt2test\awesomepad\target\scala_2.
    9.1\classes]
    java.io.IOException: Can't read [proguard.ClassPathEntry@550a17fb] (Can't proces
    s class [com/kickass/awesomepad/R$attr.class] (Unsupported version number [51.0]
     for class format))
            at proguard.InputReader.readInput(InputReader.java:230)
            at proguard.InputReader.readInput(InputReader.java:200)
            at proguard.InputReader.readInput(InputReader.java:178)
            at proguard.InputReader.execute(InputReader.java:78)
            at proguard.ProGuard.readInput(ProGuard.java:195)