For your PSP ... whatever CFW you may be running -- M33, GEN, ME, or PRO -- this is a fixed version of "usbdevice.prx" that corrects the following:
•Fixed UMD Disc mount in XMB.
•You can dump iso with correct size.
See "how2install.txt" for installation instructions specific to your custom firmware. Be careful though -- you're overwriting files in flash0. It is probably wise to create a backup first ... just in case.