For the last few days, I have been unable to invoke yast by clicking on the launcher icon 
. I soon realised that it held true for every applet that required root access for execution. Earlier, when I used to click on these launchers, the username/password window/dialog box would appear and if the user entered the correct password, the applet window ( yast2 in this case) would appear.
I’ve been too occupied with work offlate to look into this aberration. I stopped using the launchers and would directly invoke the applet from the terminal:
root@lnx:~ # yast2 &
Today I decided to look into the matter and found out that the cause of the problem was the username/password window/dialog box applet. I did some search online to find out its package name. The dialog applet is gnomesu and is part of the libgnomesu package. I tried invoking gnomesu from the terminal but got the following output:
root@lnx:~ # gnomesu
** (gnomesu:6922): CRITICAL **: No services for libgnomesu are available.
I decided to re-install/update libgnomesu to see if the problem still persists. I invoked yast2 from the command line and updated libgnomesu. Once installed, gnomesu worked fine. Now I’m able to invoke application requiring root access by clicking on the launcher icons.
Abhishek Mahanty's Blog 
I had the same problem, and it was actually caused by me making changes to the rights within the /usr folder tree.
I had accidentally chmod 777 the /usr tree and gnomesu didn’t like it.
Attempting to reinstall the package as you did didn’t fix it, but did generate the errors that alerted me to my mistake.
I chmod 755 the /usr folders and then reinstalled gnomesu and the problem was fixed.
Thanks for the post, as it pointed me in the right direction.