Dear Paolo,
The reasons can be different. First, need identify problem. You can try turn on errors in Global Configuration - Server - Error Reporting and see problem or You can give us
full FTP and admin access
and our team will try to find solution special for You, FTP and admin access You can send to our contact form.
ordasoft.com/contact-us-form
Link on website
Joomla Admin
username
password
FTP
FTP host
FTP username
FTP password
Thanks,
Taras
OrdaSoft team.