Probably you try to unlock a newly downloaded version within a directory containing an older version of VooCAT. In this case the unlocking process may fail, but it can be fixed easily: Either remove the file VooCAT_demo.exe or (on Mac) or uninstall the new version of VooCAT into a new directory.

VooCAT_demo is a backup of the demo version of VooCAT. It can be savely deleted.