In fact it's just a matter of path.
If the path is totaly wrong it is unable to open database file, if the path is Ok but is not the path to the db (ie / fogotten), an empty db is created according to the path ;-)
so now I get a more accurate error message.
Maybe, after opening the db connection you should test if it's a good db.
Now it works fine.
I am also trying to access the database on dropbox. But I don't know how to do it.
I managed to configure a .htaccess in my calibre folder so that I am redirected to my drop box (from my brower). But with cops, an empty db file is created in my calibre folder instead of accessing the dropbox db.
(install on OVH provider)
Thanks a lot.