Martin,
If you copy and paste the error message into your forum post, as well as any version information, (FGL, JAVA, ApachePOI) we might be able to assist you better.
Also if you try my example here
https://github.com/FourjsGenero/fgl_apache_poi that might help see what is missing, make sure you see the note in README about setting of CLASSPATH, particularly the annoying fact that versions are included in the filenames so it is easy to have a numerical typo.
Reuben