Sprites are not being auto selected

[Nacrevi]

I've used this spritesheet unpacker before and it's worked fine but I opened it up again and drag the sheet I wanted unpacked but nothing happens. It used to automatically select sprites and outline them but now it doesn't. I've downloaded the newest version and the one before that but still nothing. I'm not sure what's going on. I have checked in the options but there's nothing really in there that could help me.