Error: "No module named _markerlib" when installing some packages on virtualenv : <p>I can't install some packages on virtualenv because of this error.</p>

<p>I tried to install:</p>

<pre><code>pip install pyups==0.4.4
</code></pre>

<p>and </p>

<pre><code>pip install --upgrade distribute
</code></pre>

<p>and they give me the error:</p>

<pre><code>Traceback (most recent call last):
      File "&lt;string&gt;", line 1, in &lt;module&gt;
      File "/tmp/pip-build-tLx1oC/distribute/setup.py", line 58, in &lt;module&gt;
        setuptools.setup(**setup_params)
      File "/usr/lib/python2.7/distutils/core.py", line 151, in setup
        dist.run_commands()
      File "/usr/lib/python2.7/distutils/dist.py", line 953, in run_commands
        self.run_command(cmd)
      File "/usr/lib/python2.7/distutils/dist.py", line 972, in run_command
        cmd_obj.run()
      File "setuptools/command/egg_info.py", line 177, in run
        writer = ep.load(installer=installer)
      File "pkg_resources.py", line 2241, in load
        if require: self.require(env, installer)
      File "pkg_resources.py", line 2254, in require
        working_set.resolve(self.dist.requires(self.extras),env,installer)))
      File "pkg_resources.py", line 2471, in requires
        dm = self._dep_map
      File "pkg_resources.py", line 2682, in _dep_map
        self.__dep_map = self._compute_dependencies()
      File "pkg_resources.py", line 2699, in _compute_dependencies
        from _markerlib import compile as compile_marker
    ImportError: No module named _markerlib
</code></pre>

<p>I tried also to install markerlib with </p>

<pre><code>pip install markerlib
</code></pre>

<p>But the error continues.</p>
