Error everytime I try to use extract rebuild GDI tool

[El Flama Blanca]

Hey every time I try to use the Extra Rebuild GDI tool, I get this message even though the GDI is in the folder I'm dragging into the program and it's valid.

Screenshot 2025-06-05 191943.png (14.45 KiB) Viewed 363 times

Basically what I am trying to do is mod NBA on NBC. Just basic things like names, attributes and player photos.

I know I need to extract the data from the gdi files first and then I need to use a hex editor to alter the files but whenever I open up the files in any hex editor, but not sure what I do from there.

Are there certain tools I should download to make this easier?