error

root@server [~]# pip install single
Traceback (most recent call last):
  File "/usr/bin/pip", line 7, in ?
    sys.exit(
  File "/usr/lib/python2.4/site-packages/pkg_resources.py", line 236, in load_entry_point
    return get_distribution(dist).load_entry_point(group, name)
  File "/usr/lib/python2.4/site-packages/pkg_resources.py", line 2097, in load_entry_point
    return ep.load()
  File "/usr/lib/python2.4/site-packages/pkg_resources.py", line 1830, in load
    entry = __import__(self.module_name, globals(),globals(), ['__name__'])
  File "/usr/lib/python2.4/site-packages/pip-1.2-py2.4.egg/pip/__init__.py", line 9, in ?
    from pip.basecommand import command_dict, load_command, load_all_commands, command_names
  File "/usr/lib/python2.4/site-packages/pip-1.2-py2.4.egg/pip/basecommand.py", line 4, in ?
    from pkgutil import walk_packages
ImportError: cannot import name walk_packages