Search script failed (windows)

[with0out]

Vim version 7.4 (support python 2&3), using Python version 2.7.11. When using :SearchNotes, errors pops up:

notes.vim 0.33.4: Searching notes using keyword index ..
notes.vim 0.33.4: Building keyword index (this might take a while) ..
notes.vim 0.33.4: Search script failed! Context: {'stderr': ['Traceback (most recent call last):', 
'  File "O:\Vim\vimfiles\bundle\vim-notes\misc\notes\search-notes.py", line 47, in <module>', '    
import logging', '  File "D:\Python27\Lib/logging/__init__.py", line 26, in <module>', '    
import sys, os, time, cStringIO, traceback, warnings, weakref, collections',
'ImportError: No module named cStringIO'], 'exit_code': 1, 'stdout': [], 'command': 
'(python2 "O:\Vim\vimfiles\bundle\vim-notes\misc\notes\search-notes.py" 
"--database" "O:\Vim\vimfiles\bundle\vim-notes\misc\notes\index.pickle" 
"--notes" "O:\Vim\vimfiles\bundle\vim-notes\misc\notes\user" "vim") 
1>"D:\AppData\Local\Temp\VIPBD92.tmp" 2>"D:\AppData\Local\Temp\VIQBD93.tmp"'}

And following lines are in vimrc file. (because I have both python version 2&3 installed)

let $PYTHONHOME='D:\Python27'
let $PYTHONPATH='D:\Python27\Lib'

And I tried to use python's interactive shell to directly import cStringIO, no error there. However, despite this error message, search result did show up. Is there anything I need to do to get this search script working? Thanks.