Description of problem:

Every time 'yum' is invoked it fails to start with the following traceback:

Traceback (most recent call last):
  File "/usr/bin/yum", line 29, in <module>
    yummain.user_main(sys.argv[1:], exit_code=True)
  File "/usr/share/yum-cli/yummain.py", line 355, in user_main
    errcode = main(args)
  File "/usr/share/yum-cli/yummain.py", line 174, in main
    result, resultmsgs = base.doCommands()
  File "/usr/share/yum-cli/cli.py", line 572, in doCommands
    return self.yum_cli_commands[self.basecmd].doCommand(self, self.basecmd, self.extcmds)
  File "/usr/share/yum-cli/yumcommands.py", line 491, in doCommand
    ret = base.updatePkgs(extcmds, update_to=(basecmd == 'update-to'))
  File "/usr/share/yum-cli/cli.py", line 1016, in updatePkgs
    self.update()
  File "/usr/lib/python2.7/site-packages/yum/__init__.py", line 5055, in update
    for ievgrp in self.igroups.environments:
  File "/usr/lib/python2.7/site-packages/yum/__init__.py", line 1103, in <lambda>
    igroups = property(fget=lambda self: self._getIGroups(),
  File "/usr/lib/python2.7/site-packages/yum/__init__.py", line 1063, in _getIGroups
    self._igroups = yum.igroups.InstalledGroups(db_path=pdb_path)
  File "/usr/lib/python2.7/site-packages/yum/igroups.py", line 102, in __init__
    self._read_pkg_grps(db_path)
  File "/usr/lib/python2.7/site-packages/yum/igroups.py", line 114, in _read_pkg_grps
    ver = int(_read_str(fo))
ValueError: invalid literal for int() with base 10: ''

Version-Release number of selected component (if applicable):

yum-3.4.3-137.fc20
yum-langpacks=0.4.3-1.fc20
yum-metadata-parser-1.1.4-9.fc20
yum-plugin-changelog-1.1.31-20.fc20                                                                          yum-plugin-fastestmirror-1.1.31-20.fc20                                                                          yum-utils-1.1.31-20.fc20

How reproducible:

Persistent

Steps to Reproduce:
1. Open terminal
2. invoke some yum command, i.e. 'yum update'
3. 

Actual results:

Fails to start

Expected results:

Updates packages

Additional info: