I finally upgraded my system from 13.2 to Leap 42.1. There were a few problems along the way, but overall it was a smooth upgrade. I remembered to remove the nVidia drivers, but forgot to disable the nVidia repository so it installed a driver that no longer supports my trusty 8600GT. After figuring that out, networking wasn't working but just needed quickly reconfigured, same for sound. But the one thing that was stumping me was yast2 failing to load any module in GUI mode. No matter which I loaded, I would get the error:
Run command: /sbin/yast2 sound &
terminate called after throwing an instance of 'YUIPluginException'
what(): Couldn't load plug-in qt
YaST got signal 6 at file /usr/share/YaST2/modules/Wizard.rb:782
sender PID: 3605
/sbin/yast2: line 440: 3605 Aborted $ybindir/y2base $module "$@" "$SELECTED_GUI" $Y2_GEOMETRY $Y2
A quick visit to Google resulted in multiple posts stating that yast2-gtk was needed but isn't getting installed. I use KDE but let's give that a try. zypper in yast2-gtk and nothing changes. So let's try zypper in yast2-qt. This results in libyui-qt6 providing yast2-qt is already installed. I forget why now, but I did a rpm -qa | grep libyui and saw libyui6, libyui-qt-pkg6, etc. So logic would dictate at this point I need libyui-qt7 as well, so I installed that and bingo, it installed a couple of libraries and the sound module now loads. Software management started to load, but then threw up an error that qt-pkg could not be loaded. So zypper in libyui-qt-pkg7 (another package that I had the corresponding version 6 of I overlooked the first time) and I appear to be back in business.
Hope this helps someone. There's a lot of posts stating you need newer version of one package or another, but none that really specify exactly what to install.