Can't get swap trick to work

Yeah, another thread about the swap trick method, I'm at my wits end though so I'm hoping someone here can help me.

I'm trying to boot uLaunchELF to install FreeMCBoot but every attempt I have made to get uLaunchELF running so far has failed. I've opened up the disk drive, as in I'm not using a swap-key or whatever. I can swap the disk, it'll run from the backup but every time I try to boot the *.elf file which I replaced with uLaunchELF the screen goes black and then the "This is not a PlayStation disk" screen appears. It might be interesting to note that the disk keeps spinning even when it fails and that trying to boot any other non-modified *.elf from a backup has the same result.

I've done all of the following;
- Tried using the demo disk which came with the PS2, the "Bonus Demo 4" disk and Star Wars Battlefront 2 (referred to as working in the guide)
- Ripped/Burnt *.iso at 4x with ImgBurn
- Tried burning to Verbatim and generic DVD-Rs
- Tried the latest (4.39) uncompressed uLaunchELF and the one which is used in the guide
- Tried on both the model SCPH-39002 and SCPH-50002 PS2s (both oceanic PAL)
- Tried not changing the size of the *.elf but padding it to match the filesize of the original *.elf (as suggested in another thread)

Again I'd appreciate any kind of help with this as I'm getting kinda sick of burning coasters. Thanks in advance :)