If you are running into a problem where FastCUT 6 is hitting an error during optimization, saying "Class not registered" it is likely a key component in the background has lost its registration.
Simplest solution is to run a repair reinstall your FastCUT with administrator privilege. This will reinstate the missing component and allow you to optimize again.
If it continues to be an issue after this, please get in touch with us:
https://www.fastcam.com/new/contact.html