sphinx和pkg_resources的问题

Question

我在我的Ubuntu 12.04 Sphinx-1.2b3下安装了Sphinx-1.2b3。当我尝试执行时：

     sphinx-build -b html -d _build/doctrees   . _build/html

我得到以下输出：

Traceback (most recent call last):
  File "./sphinx-build", line 9, in 
    load_entry_point('Sphinx==1.2b3', 'console_scripts', 'sphinx-build')()
  File "/usr/lib/python2.7/dist-packages/pkg_resources.py", line 337, in load_entry_point
    return get_distribution(dist).load_entry_point(group, name)
  File "/usr/lib/python2.7/dist-packages/pkg_resources.py", line 2278, in load_entry_point
    raise ImportError("Entry point %r not found" % ((group,name),))
ImportError: Entry point ('console_scripts', 'sphinx-build') not found

有什么建议吗？