thank you for your answer.
firstly of all, you are right, the folder is called "MyBooks" and not "my ebooks" as I've remembered. Sorry, my fault!
I've found the problem: the folder in the sd card of my boox is named "My Books" and not "MyBooks" as it should have been.
I've changed it manually and I hope Calibre could manage this change (it's synchronizing at the moment) otherwise i'll format the card and send the books again.
by the way, is there a way to add a file type to the plug in? with this firmware version, the boox can read .doc files and i'd like to add it to the file list.
how could i do?
thank you again!