Locate your GUNZ files/folder, usually located at :
C:\Program Files (x86)\GG\GUNZ
Right-click on the “gunz” application and hit “properties” as shown below.
Proceed to the “Compatibility” tab.
Select “Run this program in compatibility mode”.
Select “Windows XP, Service Pack 3 from the drop down menu.
“Disable full-screen optimisations”
“Run this program as administrator”
Note: it may also be worth trying to check “use legacy ICC colour management” option if this does not work.
Repeat the exact same steps above with the “launcher” application, as seen below:
Hit "Apply" and OK.