On Ubuntu distro, if you see the error message in console as the following

Gtk-Message: Failed to load module "overlay-scrollbar"

whenever you run a Gnome-based applications, chances are you had ‘overlay-scrollbar’ package previously installed but now removed. However, the configuration file which came with that package remained on your system.

We can verify this with this command:

$ dpkg -l overlay-scrollbar
| Status=Not/Inst/Conf-files/Unpacked/halF-conf/Half-inst/trig-aWait/Trig-pend
|/ Err?=(none)/Reinst-required (Status,Err: uppercase=bad)
||/ Name                         Version             Architecture        Description
rc  overlay-scrollbar            0.2.16+r359+14.04.2 all                 Scrollbar overlay

rc : remove but config file still presents.

On my Ubuntu desktop, this config file resides at /etc/X11/Xsession.d/81overlay-scrollbar.

To correct this problem, we can purge ‘overlay-scrollbar’ package with this command:

# apt-get purge overlay-scrollbar

You would need to log out and log back in of your current X session (KDE, or Gnome) for the change to take effect.