Recently I'm having problem regarding to mounting a Boxcryptor Classic folder. Many solutions on the internet suggesting that .enfs6.xml should exist in order for encfs to recognized encrypted folder.
I realized that Keyfile.bcx in Boxcryptor Classic encrypted folder is .encfs6.xml file.
You just need to do this step.
Open Terminal and cd to your encrypted folder
Copy Keyfile.bcx to .encfs6.xml
cp Keyfile.bcx .encfs6.xml
if you haven't install encfs and cryptkeeper yet, you need to install it first to mount the encrypted folder
sudo apt-get install cryptkeeper encfs
I like to use command line, so i just use encfs
encfs ~/Dropbox/Encrypted-Folder ~/Private
I hope my post can help you troubleshoot and solve this problem.
You need to follow your Linux distro guide for installing cryptkeeper and encfs if apt-get is not your distro package manager.