Hello,
The human task is run from the compiled sources that come within the installation. So i think you have to make sure that whatever jdk is used to compile the sources (the compilation takes place when you run target start.human.task check it out in the build.xml, task javac) the same or higher version of jre must run the classes. There might be a conflict or mix up with the JREs / JDKs you have installed. If that is the case I would advice to uninstall them all and just install one version, if it is possible.