I cannot make a working build (installation)

I am doing a project for an honors-level programming class, and my group's project deals with the MIT App Inventor. For the time being, all I need to do is install it by following the github instructions and taking a screenshot of the working build, but I cannot get my build to work. Things are fine up until I have to build AppInventor. when I input "ant" it throws a bunch of errors at me.

The rest of my group got their build working fine by following the same instructions, so I am stumped. Please help if you are able to.

This error happens when you download the sources using GitHub's download functionality rather than cloning the repository using git. Cloning the sources is necessary because 1) you need to have the git submodules information, which GitHub drops from the ZIP export, and 2) the git history is used to generate App Inventor's version number, which is the step that is failing here.