from Dark_AleX:

Just a little update to the fatmsmod patch, it stopped working in 5.00 due to a sony file changing its name.

Instructions: decrypt 3.71 using psardumper (square option).
Copy the file fatmsmod.prx in the root of memory stick.

Copy FATMS371 to /PSP/GAME or /PSP/GAME5XX. Run the program and done.