root@mybox:~/arc3# /root/mz/bin/mzscheme -m -f as.scm
  -bash: /root/mz/bin/mzscheme: No such file or directory
  root@mybox:~/arc3# cd /root/mz/bin/
  root@mybox:~/mz/bin# ls
  mzc  mzpp  mzscheme  mztext  pdf-slatex  planet  plt-web-server-text  setup-plt  slatex  swindle  tex2page
  root@mybox:~/mz/bin# ./mzscheme -m -f /root/arc3/ac.scm
  -bash: ./mzscheme: No such file or directory
  root@mybox:~/mz/bin#
  root@mybox:~# cd /root/plt/bin/
  root@mybox:~/plt/bin# ls
  drscheme   mred  mzpp      mztext      planet     plt-web-server       setup-plt  slideshow  tex2page
  help-desk  mzc   mzscheme  pdf-slatex  plt-games  plt-web- server-text  slatex     swindle
  root@mybox:~/plt/bin# ./mzscheme
  -bash: ./mzscheme: No such file or directory
  root@mybox:~/plt/bin# ./mzscheme -m -f /root/arc3/as.scm
  -bash: ./mzscheme: No such file or directory
  root@mybox:~/plt/bin#

You're going to need to get help on the PLT Scheme user mailing list for this one. (This is the first mailing list listed at the top of http://www.plt-scheme.org/community.html)

Tell them what operating system you're running, including the output of "uname -a", and which distribution of PLT Scheme you downloaded. Mention you need to run PLT Scheme version 372 specifically. No need to include the "-m" or "-f" options or to mention Arc, just show them the output of when you're in the bin directory and you type just "./mzscheme"

Then, once you have mzscheme working, we may be able to help with any Arc problems you have... :-)