Oh, got it working!
DiskCopy was in wrong folder, so I copied it to System folder. But i am trying to write to PC DD floppy, but I always get an error at the end. Is it because of floppy size? I know that amiga floppy size is 880kb and PC DD is 720kb? Should I try an HD disk?
PS. I have 1MB ram and external disk drive.
Thanks -Eemil