The jet.engine.gui V4GUI was designed to run in XP and Vista operating systems. If you use another operating system different than the one mentioned here, you will encounter issues.
I recommend downloading the following PDF file which explains how to deal with the software and its working procedure. If by any means you encounter issues, then it means you're probably running the software in an unsupported environment or the software has bugs in the code. Of course, causes can be multiple, but these ones are most likely to happen frequently.