There's one thing to avoid when GPxpatch has been installed:
After installation, GPxPatch doesn't create any shortcut on the desktop.
If you don't take care, could do a copy and paste of gpxpatch executable from the gp4 folder to your desktop. In that case, Gpxpatch will search GP4 in the "desktop" folder.
The only good way to do a shortcut is really to right-clic on the Gpxpatch exe in the gp4 folder and choose "make a shortcut" and then to displace this shortcut on your desktop.
Hope it is your matter.