Turn on "Settings" / "Verbose Messages" and see if you get any additional output. Let us know the results using "Help" / "Report a Bug".
If you have the latest version of jGRASP, you can skip the wedge and run it in a pure Java mode from the command line by going to the jGRASP installation Contents/Resources/jgrasp directory and running java -jar jgrasp.jar -pj . The only problem is that your I/O will most likely be buffered unless you turn buffering off in your code.