unfortunately, we stopped supporting Boxcryptor Classic on new platforms, such as Windows 10, Mac OS X 10.11 "El Capitan", iOS9 etc.
Furthermore, we discontinued to support Boxcryptor Classic since 2017. I am sorry for the inconvenience.
Of course we tried hard to keep Boxcryptor Classic alive as long as possible.
But since Dropbox is discontinuing their old Dropbox API v1, Boxcryptor Classic will also no longer be able to connect to Dropbox on mobile devices.
Please have a look here: https://blogs.dropbox.com/developers/2017/09/api-v1-shutdown-details/
The API v1 was supported by us till February 28th, 2018:
(scroll down the page)
I would strongly suggest you to upgrade to Boxcryptor, because this version is supported on the new operating systems.