Presumably you forgot to specify that owner should inherit from superadmin.
If anything, see the FAQ on resetting to factory default settings. And, in the future, don't make an owner group. Superadmin is sufficient enough, and Garry's Mod treats it as root, as it should be. Scripts that call Player:IsSuperAdmin() will allow anyone in the superadmin group root-level permissions which are usually intended for server operators (ie people you trust).
