Please check that the "RLHostService" is running. You can take a look in the Task Manager > Services. If it has stopped working then right-click Start and reopen your program.
If it still does not work then please collect the following data and contact Reallusion Support.
1. Confirm whether the folder exists "C:\ProgramData\Reallusion\CMS", compress it as a zip file.
2. The detail log from "Dbgview.exe".