Just out of interest, not really any issue here - when creating subdirectories in my VST folder, are there some names that are not allowed? I decided to tidy up my many VST instruments, and put a bunch of synths into a subdirectory I called “ethereal”. I then refreshed the plugin manager list and got a “serious error” notification. Upon restarting Cubase, none of those syths would load, but all other synths and effects in all other subdirectories were OK. I changed the subdirectory name to “synths” and suddenly all is fine. Just to check this, I changed it back to “ethereal” and the same thing happened again.
Do you mean in the Plug-in Manager? I would expect some “system forbidden” characters (like /*, etc.) might be skipped.