can't reconfigure lightdm with dpkg. Please help

[milius]

I'm reverting a gdm3 configuration but this is what i get:

sudo dpkg-reconfigure lightdm
insserv: warning: script is corrupt or invalid: /etc/init.d/../rc2.d/S01shm_load

Please, help me

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: lightdm 1.18.3-0ubuntu1.1
ProcVersionSignature: Ubuntu 4.8.0-46.49~16.04.1-generic 4.8.17
Uname: Linux 4.8.0-46-generic x86_64
NonfreeKernelModules: wl
ApportVersion: 2.20.1-0ubuntu2.5
Architecture: amd64
CurrentDesktop: Unity
Date: Wed Apr 5 20:28:24 2017
InstallationDate: Installed on 2017-03-19 (17 days ago)
InstallationMedia: Ubuntu 16.04.2 LTS "Xenial Xerus" - Release amd64 (20170215.2)
SourcePackage: lightdm
UpgradeStatus: No upgrade log present (probably fresh install)