PS2 softmod help

[kursedkey]

I am trying to soft mod my PS2 FAT using the Free McBoot method, but instead of using 007 agent under fire, I am using Metal Gear Solid 3. I replaced NETDOWN.ELF with ulaunchelf's BOOT.ELF, as described in the tutorial on the site. When I swapped the disk using a homemade slide card, and tried to load ulaunchelf, but the PS2 recognized the fake disk, and gave me the disk read error. I just want to know what i did wrong here. I was using the original MGS3, not the subsistence version. as I said, my PS2 is the FAT model. Thanks in advance.

EDIT: I tried to do it again, but I used the uncompressed BOOT.ELF instead, and I got the same results, with it asking for a PS2 or Playstation format disk. Again, any help would be great. Thank you.

EDIT 2: My PS2 model number is SCPH-50010/N. I hope this helps.