boot.img not found

Hi , when trying to build the iso (according to the remasteringhowto)
I get
mkisofs: Uh oh, I cant find the boot image 'KNOPPIX/boot.img'

Why is that?

Is it where you stated it is via the -b option?

Thank u for answering,
Yes. I followed the remastering howto and until that all seemed to be ok