@Jake Moints: Some ELF-Launchers are simply not reliable and fail often. AR-Maxs MediaPlayer is one example for such a case.
Thatīs why you need to use the FCEU.ELF and start the installer through this.
The AR-Mediaplayer have some other issues (such as recognizing more than 5ELFs --> First ELFs, which were copied to the device are 'seen'). Thatīs why it is recommented to put the files on a clean USB-Stick.
Anyway, you got it working in another way.
I just wanted to sort out some irritations.
PS2 V7/DMS3 V2 (FW:2.4b7); Seagate Baracuda 200GB
PS2 V7/CC1.0 (FW:34 hacked v2 BM:2.1.6); Maxtor DiamondMAX9 PLUS 160GB
PS2 SCPH-30004R; NoMod+NoLaser
3xSony MC 8MB
MAX/Datel 16MB with Boot-CD
Custom FMCB 1.8b+ Beta-Build, my AIO 0.5, Sony&xRhino-Linux