This had me going for a long time trying to figure out what the heck was going on. Any time I tried to run an ant task from inside eclipse I would get this "waiting for virtual machine to exit" message and ant would just hang. Nothing in the console at all to tell me what was wrong.
If I ran the same thing from the command line, everything worked fine, so it must be some eclipse setup thing that's screwed up.
To make a long story short, for some reason, the ant home directory was not pointing to the ant install in eclipse.
To fix, go to window | preferences | Ant | runtime | Ant Home... and enter the path to the embedded ant install (for me, this is: C:/Program Files/eclipse/plugins/org.apache.ant_1.7.0.vblahblah
For some reason, it was pointing into my workspace directory.