Those warning messages are probably not important. Typically, they get hidden away in one of the “.xsession-error*” files.
You might do better to first use “su -” to become root (or, start a root terminal in some other way), and then directly run “gparted” from the command line.
I don’t normally use Gnome. When I start “gparted” from a root command line in KDE, it does work. When I start from the menu in the live rescue CD (using XFCE), it never starts. If I start from a root terminal in XFCE, it does start but it is useless because XFCE mounts all of the partitions that I want to change.
In my experience the best way to use “gparted” is to login to Icewm, then start “gparted” from a root terminal.
You likely stumbled on Bug 920510 (I don’t remember exactly what it did in 13.2).
It is fixed for Leap and Tumbleweed, but likely it didn’t trickle down to OS 13.2
The best workaround is to start it from a root terminal ( “su” > root pw > “gparted”), as nrickert suggested.