Unpacking and repacking system.img error

Hello, I'm trying to unpack and repack a system.img file using cygwin and the "simg2img" and "make_ext4fs" binary file. I am using cygwin because Linux is too much for VirtualBox and I have a bootcamped Mac so I don't have a lot of space on my Windows partition. My problem is when I run this: $./simg2img system.img sys.raw it returns with this -bash: ./simg2img: cannot execute binary file: Exec format error I really don't understand why this is happening and I checked the Ubuntu forums many times but I still cannot find anything.

http://forum.xda-developers.com/show....php?t=1588461
^^ Trying to follow that guide.

Thanks in advance :)