pip issue

/usr/local/bin/pip run on Fri Oct  2 16:22:14 2009
Exception:
Traceback (most recent call last):
  File "/Library/Python/2.5/site-packages/pip-0.4-py2.5.egg/pip.py", line 274, in main
    self.run(options, args)
  File "/Library/Python/2.5/site-packages/pip-0.4-py2.5.egg/pip.py", line 431, in run
    requirement_set.install_files(finder, force_root_egg_info=self.bundle)
  File "/Library/Python/2.5/site-packages/pip-0.4-py2.5.egg/pip.py", line 1784, in install_files
    if req_to_install.check_if_exists():
  File "/Library/Python/2.5/site-packages/pip-0.4-py2.5.egg/pip.py", line 1641, in check_if_exists
    dist = pkg_resources.get_distribution(self.req)
  File "/System/Library/Frameworks/Python.framework/Versions/2.5/Extras/lib/python/pkg_resources.py", line 264, in get_distribution
    if isinstance(dist,Requirement): dist = get_provider(dist)
  File "/System/Library/Frameworks/Python.framework/Versions/2.5/Extras/lib/python/pkg_resources.py", line 156, in get_provider
    return working_set.find(moduleOrReq) or require(str(moduleOrReq))[0]
  File "/System/Library/Frameworks/Python.framework/Versions/2.5/Extras/lib/python/pkg_resources.py", line 417, in find
    raise VersionConflict(dist,req)     # XXX add more info
VersionConflict: (virtualenv 1.3.3 (/Library/Python/2.5/site-packages/virtualenv-1.3.3-py2.5.egg), Requirement.parse('virtualenv==1.3.4'))