Www.newsoftwares.net/folderlock/faq/#faqs_13
Copy and paste:
If you have Encrypted your data with the older version Folder Lock 6, you can open these Lockers (*.flk files) with the new version. Please note that this version only allows you to encrypt and decrypt your old lockers, you cannot, however, change password for old Lockers(*.flk files) with the new version.
https://ccm.net/forum/affich-588014-lost-files-in-folder-lock-6