Knowing your computer specs and project specs would help a great deal in assisting you. But for now, here's a few ideas.
1. Make sure you are using latest FCPX and latest Color Finale versions.
2. Color Finale requires a graphics card with OpenCL V1.2 or later.
3. Color Finale has some issues with NVidia graphics cards. The support site has more info on this.
4. If all these items are good then try restarting FCPX while holding down Option and Command keys to trash preferences.
Have you been able to export or render another clip in a different project using Color Finale? If so, you may have a corrupt project or render files in that project causing the error. You can try to "delete generated library files" through the menu setting in FCPX to see if this helps.
Finally, leave a support request email at Color Finale if you think everything outlined above is OK.