Questa la risposta ricevuta dal supporto DropSync a seguito della mia richiesta di mancato funzionamento dell'applicazione
Di bene in meglio !!!!!
Roby
Hi,
Do you use the app to sync a folder on the external SD card?
It appears that many devices running Android 4.4 do not allow non-system apps to write to the external SD card. Apps can read but cannot write, or to be exact a non-system app can write to the SD card but only to one dedicated folder, not anywhere outside of that folder. This problem started with Android 4.4 update and affects all non-system apps. If our app can't write to a folder, it cannot sync it. Unfortunately it's not fixable by us. Apps cannot workaround system restrictions. Only the device manufacturer and Google can fix it. Basically with Android 4.4 update they break write access to the external SD card.
You can fix it yourself but you'd need to root your device, then modify a system config file, and potentially void the warranty by doing so.
Here is a good article explaining the situation: External Blues: Google Has Brought Big Changes To SD Cards In KitKat, And Even Samsung Is Implementing Them
This issue affects the external SD card only. You should be able to sync folders in the internal storage just fine.
Regards,
Trung