could you please try to reproduce the error in debug mode. To start Boxcryptor in debug mode, quit Boxcryptor and execute the shortcut "Boxcryptor (Debug)". You can find this shortcut in the Boxcryptor installation directory (e.g. C:\Program Files (x86)\Boxcryptor).
Boxcryptor will then create a file called "Boxcryptor.svclog" on your Desktop. Please send this file to firstname.lastname@example.org
Note: The debug log can contain sensitive information (e.g. filenames), but it will never containt any file content.