I've got JDEE 2.3.4 and Apache Ant 1.5. The problem I was having was that I'd get this error message whenever I tried to do C-c C-v C-b (i.e. build my project using ant):
Anyhow, after some poking around, I discovered this post (http://article.gmane.org/gmane.emacs.jdee/3910/match=+buildfile+exist) which helped me fix my issue. I went into jde-ant.el and removed two instances of "delimiter" and now everything works super duper.