I and another have the free BoxCryptor account connected to Dropbox and I try to grand access to the other user to a new empty folder and get "FAILED TO CHANGE PERMISSIONS"
How to reproduce an PC Win 7:
Click BoxCryptor icon to open BoxCryptor
Create new folder: Click "New Folder" button
Click in the BoxCryptor dialog the green button "Encrypt"
A new folder with green letters is created named "New Folder"
RClick "New Folder"
Select BoxCryptor and then Manage Permission
The Manage Permission dialog is displayed
Click Add User
Key in the mail address for how should have access to the folder
Click on the list so OK button is enabled (small bug)
The name and the mail address is added to the list
"Preparing" message is displayed long time
And then red box show "FAILED TO CHANGE PERMISSIONS"
Same "FAILED TO CHANGE PERMISSIONS" if I do the same but in dropbox share the folder and the other accept the sharing.