Usb iso loader psp 6.60 download

Ok, its not often I ask a question, so bear with me. I have reserched on the topic aswell, so please don't give me answers like "google is your friend" and stuff like that.

Anyway, today I decided to try out the usb iso loading function on Prometheus iso loader,because I wanted to play games like gran turismo as an iso for faster loading, but my memory stick is full. I got everything set up allright, the iso files show up on the screen etc, but when I try to load them:

M33 driver - spits me back to the XMB (yes, I put isofs_500.prx inside the folder)
NP9660 - freezes and shuts down.

This happens on the iso files I've tested so far, which are "Gran Turismo", "Coded Arms" (the first one, its so much better than "contagion"!) and "Sid Meier's Pirates!". I have also tried it with game plugins disabled.

Is this a fixable issue? I can do without it, but it would be nice to have if you know what I mean

Thanks in advance!

my psp is a 3000 running 6.60 PRO-C