Error File not open for reading

I am using the following script to add a copy right to all the files in the directories and subdirectories for a give directory passed as first argument ,am running the script as follows but running into below error... can anyone provide inputs on ohw to fix it?

ERROR:-

C:\Dropbox\copyrights>python Add_copyright.py .
Traceback (most recent call last):
  File "Add_copyright.py", line 70, in <module>
    prepend_file(fullname, dirpath)
  File "Add_copyright.py", line 50, in prepend_file
    shutil.copyfileobj(in_file, out_file)
  File "C:\Python27\lib\shutil.py", line 49, in copyfileobj
    buf = fsrc.read(length)
IOError: File not open for reading

CODE:-

import fnmatch
import os
import shutil
import sys
import tempfile

file_patterns_to_match = ['*.c','*.h','*.cpp','*.txt']

headertext = """/*
 * Copyright (c) 2012-2013, The Linux Foundation. All rights reserved.
 *
 * Previously licensed under the ISC license by Company, Inc.
 *
 *
 * Permission to use, copy, modify, and/or distribute this software for
 * any purpose with or without fee is hereby granted, provided that the
 * above copyright notice and this permission notice appear in all
 * copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL
 * WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED
 * WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE
 * AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL
 * DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR
 * PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER
 * TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
 * PERFORMANCE OF THIS SOFTWARE.
 */
"""

# make any newlines in headertext match the system line ending
headertext = headertext.replace('\n', os.linesep)

def want_this_file(fname):
    for pat in file_patterns_to_match:
        if fnmatch.fnmatch(fname, pat):
            return True
    return False

def prepend_file(fullname, path):
    # with statement means temp file is written and closed at end of with
    with tempfile.NamedTemporaryFile(dir=path, delete=False) as out_file:
        # get the name immediately
        temp_fname = out_file.name

        try:
            # use binary mode to avoid newline translations
            with open(fullname, "rb") as in_file:
                out_file.write(headertext)
                shutil.copyfileobj(in_file, out_file)
        except Exception:
            # on any error, clean up temp file and re-raise exception
            try:
                os.remove(temp_fname)
            except Exception:
                print("unable to clean up temp file: " + temp_fname)
                pass
            raise
    # rename temp file to fullname, clobbering original
    os.rename(temp_fname, fullname)


start_directory = sys.argv[1]

for dirpath, dirnames, filenames in os.walk(start_directory):
    for fname in filenames:
        if want_this_file(fname):
            fullname = os.path.join(dirpath, fname)
            prepend_file(fullname, dirpath)