Problem with NesterJ for PSP

[SgtDrPeppers]

I'm running NesterJ on a PSP 3000 and I'm trying to play Super Mario Bros. I want to set the controls so I can use the D-Pad but every time I go into the Key Config menu I can't assign anything to the D-Pad.

The D-Pad clearly works because I can navigate the menu using it, I just can't find a way to assign movement to it. Anyone had this problem or got any ideas?

Thanks
SgtDrPeppers