Hi Wipster,
You have a couple options here:
Ilias Log File (specified in ilias.ini.php), check what is in there, this is log output from Ilias
Apache Log File (specified in your virtial host, possibly /var/log/apache2/error.log), stuff related to how apache handles requests
Turn debug/devmode on for the client you are working on:
in /path/to/ilias/data/<CLIENTID>/client.ini.php .. add in the following under [system]:
DEBUG = "1"
DEVMODE = "1"
Hope this helps, I tried the example plugin on Ilias 5.0.6 and it appeared in the list of plugins right away.
Regards,
Adam