package sbackup-gtk (not installed) failed to install/upgrade: subprocess installed post-removal script returned error exit status 127

PROBLEM
After login the desktop was empty (no more menus).

GUESS
I thought that package was the problem but google doesn't think so.

SOLUTION
I had to CTRL+ALT+F1, do some magic I don't understand and fixed it accidentally.
* DISPLAY=:0 sudo startx //idk what this does but it's good stuff
* CTRL+ALT+F7
* create a temp folder on the desktop
* CTRL+ALT+F1
* stop the "startx"
* rm .Xauthority //this kills the login loop problem
* exit
* CTRL+ALT+F7
* login, finally

QUESTION
Can you please enlighten me on what PROBLEM happened ?

ProblemType: Package
DistroRelease: Ubuntu 16.04
Package: sbackup-gtk (not installed)
ProcVersionSignature: Ubuntu 4.4.0-112.135-generic 4.4.98
Uname: Linux 4.4.0-112-generic x86_64
ApportVersion: 2.20.1-0ubuntu2.15
Architecture: amd64
Date: Tue Mar 13 01:04:16 2018
DuplicateSignature:
 package:sbackup-gtk:(not installed)
 Removing sbackup-gtk (0.11.6-0ubuntu1) ...
 /var/lib/dpkg/info/sbackup-gtk.postrm: 11: /var/lib/dpkg/info/sbackup-gtk.postrm: gtk-update-icon-cache: not found
 dpkg: error processing package sbackup-gtk (--remove):
  subprocess installed post-removal script returned error exit status 127
ErrorMessage: subprocess installed post-removal script returned error exit status 127
InstallationDate: Installed on 2015-05-13 (1034 days ago)
InstallationMedia: Ubuntu 14.04.2 LTS "Trusty Tahr" - Release amd64 (20150218.1)
RelatedPackageVersions:
 dpkg 1.18.4ubuntu1.3
 apt 1.2.25
SourcePackage: sbackup
Title: package sbackup-gtk (not installed) failed to install/upgrade: subprocess installed post-removal script returned error exit status 127
UpgradeStatus: Upgraded to xenial on 2016-08-01 (588 days ago)