I had issues with Gp4 Browser 1.2 as well but not the same as yours. This what I did to fix my issue. OS: Windows 10.
-install gp4 browser on your desktop.
-create a folder on your desktop and name it gp4.
-go to where you have gp4 installed and copy the gp4.exe and the folder "menudata" and paste into the folder created on the desktop. (step2)
-now open gp4 browser and set gp4 path to the folder created on desktop. Gp4 browser should be working now.
-make/apply changes.
-copy and paste menudata folder from the desktop into your gp4 install folder.
Hope it helps.
Glenn