Hi,
finally I found a way to make documents tab work properly.
After Zimbra installation and Zimbra user creation, typing the following command zimbra will initialize Documents for a specific user:
/opt/zimbra/bin/zmprov in
name.surname@domain.com
where in stands for initialize and
name.surname@domain.com is the user login followed by user domain.
Hope this helps who will face my problem in the future.
Regards,
Denis Maggiorotto