: Ensure ul.cfg is located in the root of your USB drive, not inside a folder like /DVD or /CD.
The ul.cfg file serves as a master database or "game list" for PS2 games that have been split into chunks. This splitting is necessary because:
: For games under 4GB, you should ideally use the standard ISO format in the /DVD folder and manage them with OPL Manager instead of splitting them. PS2 - How to use USBUtil | Page 2 - PSX-Place