If you are using diskless HDL, You should patch your HDL elf properly <period>
Regardless of PS2 model, if you are not using discs to boot it, don't patch it with the damned disc stof option as it only gives problems. ;)
Its possible your friends PS2 and yours dont have the same Mobo/Bios. I have 2 V4 NTSC console and the mobos are not the same.
Or your NA is a different version, has some issue with the connection, etc.