Changing filenames from Greeklish => Greek (subprocess complain)

[Νικόλαος Κούρας]

 /home/nikos/public_html/cgi-bin/metrites.py in ()
    217                 template = htmldata + counter
    218         elif page.endswith('.py'):
=>  219                 htmldata = subprocess.check_output( '/home/nikos/public_html/cgi-bin/' + page )
    220                 template = htmldata.decode('utf-8').replace( 'Content-type: text/html; charset=utf-8', '' ) + counter
    221                 
htmldata undefined, subprocess = <module 'subprocess' from '/opt/python3/lib/python3.3/subprocess.py'>, subprocess.check_output = <function check_output>, page = 'files.py'
 /opt/python3/lib/python3.3/subprocess.py in check_output(timeout=None, *popenargs=('/home/nikos/public_html/cgi-bin/files.py',), **kwargs={})
    584         retcode = process.poll()
    585         if retcode:
=>  586             raise CalledProcessError(retcode, process.args, output=output)
    587     return output
    588 
global CalledProcessError = <class 'subprocess.CalledProcessError'>, retcode = 1, process = <subprocess.Popen object>, process.args = '/home/nikos/public_html/cgi-bin/files.py', output = b'Content-type: text/html; charset=utf-8\n\n<bod...n position 74: surrogates not allowed\n\n-->\n\n'
CalledProcessError: Command '/home/nikos/public_html/cgi-bin/files.py' returned non-zero exit status 1 
      args = (1, '/home/nikos/public_html/cgi-bin/files.py') 
      cmd = '/home/nikos/public_html/cgi-bin/files.py' 
      output = b'Content-type: text/html; charset=utf-8\n\n<bod...n position 74: surrogates not allowed\n\n-->\n\n' 
      returncode = 1 
      with_traceback = <built-in method with_traceback of CalledProcessError object>


The above error message happened when i tried to reanme one of my filenames from

its greeklish name to greek charcters.

files.py is a script that allows users to downlaod fiels form my server.
But i wish to presnt filename sin Greek and not in Greeklish

http://superhost.gr/?page=files.py
as it is now.

What can i do to make pth script accept greek filenames too?
Why does subprocess is complaining?