simple renaming files program

[blur959]

Hi, all, I am working on a simple program that renames files based on
the directory the user gives, the names the user searched and the
names the user want to replace. However, I encounter some problems.
When I try running the script, when it gets to the os.rename part,
there will be an error. The error is :
 n = os.rename(file, file.replace(s, r))
WindowsError: [Error 2] The system cannot find the file specified

I attached my code below, hope you guys can help me, Thanks!

import os
directory = raw_input("input file directory")
s = raw_input("search for name")
r = raw_input("replace name")

for file in os.listdir(directory):
    n = os.rename(file, file.replace(s, r))
    print n