PS2MAME on USB

I understand that MAME for the PS2 is old hat now, but I'm trying to get it to work on USB, NOT CD.

I have created a MAME ISO on my USB stick. The ISO works perfectly if I load it from CD or DVD in the drive.

Trouble is, it doesn't work. Can somebody PLEASE explain how to get MAME to work on USB? OPL says the ISO is fragmented, and won't run. :(

If I turn off the fragment warning in OPL, the screen flashes a couple of times, then goes white. It's driving me mad!

The USB drive runs everything else perfectly. Stella, OPL, FreeMcBoot runs, my internal HD works with HD Loader. I can run Mame from a disc, but I'd like to be able to drop / swap ROMs into the ROMs folder, then pop my USB into the PS2. Burning a new coaster every time I want to do this is frustrating!

In the "how to install mame emulator" thread, LopoTRI gives a method, but it doesn't work for me. I followed what he said exactly. Like I say above, using his method, I can create a MAME ISO on my USB stick, but OPL 0.9 won't play.

PLEASE, PLEASE help!! Somebody...? Is there Anybody that knows how to do this?

I don't know how to get it to run from USB. But instead of burning CDs you can generate several different .isos with a different set of 60 roms (or whatever size list you feel like scrolling through). Each of these can then be put on the hard drive and run by OPL from the hard drive. You never have to burn a CD. The images are small, around 128MB, so you can have many different .isos without using much of your HDD space.