Image_assist do not insert HTML code

Hi all!

I installed all extensions of Image module, enabled them for registered users and configured them.
Input format set to full HTML with <img> allowed.
I uploaded some images and can click on the button to add an image into a document (e.g. a book page).
I can browse images, set their properties but I cannot see any image inserted into my page:
- If I choose Filter Tag mode, Image_assist inserts a strange code (custom?) but in View mode no image is displayed.
- If I choose HTML code mode, Image_assist does not insert any HTML code.

This behaviour is reproducible.
All trials have been made as Administrator.

What can I check? Did I missed something?
Thanks!
Antonio