Hi Emmanuelle.
Before all, thanks for your help.
The packages seems to be installed because I created them from the "Package Manager" page. However I have uninstalled and installed them again, but my problem remains.
I have checked my code a lot of times, even comparing with other uninstalled packages (like "dotlrn-chat" which can be installed correctly) so I suppose my problem must be a simple overlooked detail.
Are there more documentation, apart from the API, explaining the process of constructing a portlet?
Thanks in advance.