SP Client Document & Project Manager (File not visualized)

Hi,
I installed the plugin (WordPress 3.8.1, theme Twenty Twelve, on Windows 7 os with Apache, all seems to be ok..) and I can see correctly the plugin in the blog page. I can also create new directories and delete them, but when I do an upload of a file, it appears (correctly) only in the directory of the file system (hard disk) but is not shown in the file list of plugins (that appears empty).
The icon of the uploaded file on the hard disk, has a small padlock over (not sure if this is ok with the general permissions needed, but I seem to be ok).
In addition, when into the administration page, I download the “archive file”, the plugin creates a zip file, save it in the root directory of the hard disk where the file is and the browser download it correctly, but the zip file is empty.
What could be the error that does not allow to view files in the plugin page?
thanks a lot
Daniele