Have you defragmented the disk? Please do not use Power Defragmenter, since it seems occasionally prone to leave fragmented regions behind after it defragments your disk.
Originally Posted by kairi033
Auslogics Disk Defragmenter is a better choice.
If your PS2 is a slimline, you could also try to unplug your disk and re-plug it back in, whenever the PS2 seems to be waiting for something. Give the PS2 some time, like about 10 seconds before you do that.
PS2ESDL resets the I/O Processor (IOP) about 2 times as your game gets loaded, so you might need to replug your disk twice.
There is a problem with the USB driver, causing some USB devices to be incompatible with some slimline consoles.
If none of these solutions help you, I'm afraid that you might have a truly incompatible USB device.
SCPH-10000 S. MINOKAMO v1.01 (Defunct)
SCPH-10000 S. KISARAZU v1.00 (faulty)
SCPH-15000 S. KOHDA (With warranty seal!) :D
DESR-5100 S. EMCS