How can I resolve the error shown in the photo.
I have changed my desktop to gnome and managed to update but when I use this desktop my OS refuses to update. When I update with Plasma KDE, this works.
Really not sure how do you do it using the software-center, but you can install it from the command line using:
sudo apt-get install wireshark
and then it may ask you whether to install unauthenticated packages, don't worry, this warning usually means they are not from the main Ubuntu repositories, but in most cases reliable to install, press