You can try and solve it in several ways.
First of all did you try and check if the C$ or any other share on the C:\ drive contains permissions for this group?
Make a backup of the folder so in case of failure you can restore everything and, above all, the permissions.
After having created the backup uncheck the propagation and select to KEEP existing permissions so you can delete the wrong one.
Another option may be to set explicit permission on the NETLOGON folder in order to DENY access to the given group.