That's impossible to say without seeing the build file. If that really has more than 852 lines (which that error message leads me to believe), then I don't think anyone here can help, because that's WAY too much to read and try to make sense of. Have you tried it with a minimal build file? A basic build file that compiles code and generates javadocs for it shouldn't need more than 50 lines or so, and quite possibly fewer than that.
BTW, if you succeed in generating the JavaDocs I doubt they'll be anything more than minimal and useless, given your current JavaDoc comments, but maybe the exercise is simply to learn how to use the JavaDocs generation tool.