All your files which are used 'In-game' need to be 100% fragment-free (so one file must be of one big continous chunk).
Defragment your files with the tool from 'Auslogics'.
It is reliable for this (not like Powerdefragmenter, or how it was called...).
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