There is clearly another root cause here that may be indicative of other issues that simply editing the registry won't address. My guess is that someone moved the folders manually instead of properly removing the roles and re-adding them to the system after a blank no_sms_on_drive.sms file was place on the C volume.
I strongly suggest you do this now (remove the roles and site system, add the file, and then reinstall the roles). Anything else is just asking for issues down the road.