pip: pip freeze:Invalid requirement, parse error at "'-ipap11h'"

• Pip version: 8.1.2
• Python version: 2.7.5
• Operating System: Centos 7

Description:

While trying to run pip freeze I got this message:

Exception:
Traceback (most recent call last):
  File "/usr/lib/python2.7/site-packages/pip/basecommand.py", line 215, in main
    status = self.run(options, args)
  File "/usr/lib/python2.7/site-packages/pip/commands/freeze.py", line 85, in run
    for line in freeze(**freeze_kwargs):
  File "/usr/lib/python2.7/site-packages/pip/operations/freeze.py", line 47, in freeze
    dependency_links
  File "/usr/lib/python2.7/site-packages/pip/__init__.py", line 264, in from_dist
    req = dist.as_requirement()
  File "/usr/lib/python2.7/site-packages/pip/_vendor/pkg_resources/__init__.py", line 2562, in as_requirement
    return Requirement.parse(spec)
  File "/usr/lib/python2.7/site-packages/pip/_vendor/pkg_resources/__init__.py", line 2833, in parse
    req, = parse_requirements(s)
  File "/usr/lib/python2.7/site-packages/pip/_vendor/pkg_resources/__init__.py", line 2781, in parse_requirements
    yield Requirement(line)
  File "/usr/lib/python2.7/site-packages/pip/_vendor/pkg_resources/__init__.py", line 2790, in __init__
    raise RequirementParseError(str(e))
RequirementParseError: Invalid requirement, parse error at "'-ipap11h'"

What’s the ‘ipap11h’