MacOS High Sierra 10.13 introduced a new feature that requires user approval before loading new third-party kernel extensions.
We believe this might be the reason of the error message you are getting.
To approve BestCrypt modules to be loaded, please navigate to Security & Privacy in System Preferences and click Allow. Use this screenshot as a reference:
Once approved, the modules will be loaded without further user interaction.
The system might suggest that approval requires a restart, but it should be enough just to relaunch BestCrypt and wait around 30 seconds for the modules to load.