There is a conflict between cPanel and LiteSpeed and each of both said the other one did a missconfiguration. This conflict goes back to year 200*, but this error isn't a real error, but it is confusing everyone. LiteSpeed displays an error_document (403,404,500, ....) and cPanel expects this error_document in the domain_root, but there is none. To solve it place the attached (compressed) 403.shtml in the domain_root and you will never get such error message.