Possible problems:
1. You're not actually including the jar file. What kind of error do
you get? Something along the lines of "Setter not found", which would
indicate the jar is simply not included by ant. Double check the
classpath. I always use the following syntax:
lib/**/*.jar
possibly that's the problem.
2. You are including the jar, but annotation processing is off. This
would happen if you're compiling with javac5 or earlier. Use javac6
and make sure there's nothing like -proc:none being passed as
argument.