问题：有时GAE-python在我的OSX上本地运行。有时却没有。如果没有，我会收到以下错误：
警告2013-12-22 02：03：24,811 api_server.py:331]无法初始化图像API;你很可能错过了Python“PIL”模块。
Traceback (most recent call last):
File "/Applications/GoogleAppEngineLauncher.app/Contents/Resources/GoogleAppEngine-default.bundle/Contents/Resources/google_appengine/dev_appserver.py", line 197, in <module>
_run_file(__file__, globals())
File "/Applications/GoogleAppEngineLauncher.app/Contents/Resources/GoogleAppEngine-default.bundle/Contents/Resources/google_appengine/dev_appserver.py", line 193, in _run_file
execfile(script_path, globals_)
File "/Applications/GoogleAppEngineLauncher.app/Contents/Resources/GoogleAppEngine-default.bundle/Contents/Resources/google_appengine/google/appengine/tools/devappserver2/devappserver2.py", line 872, in <module>
main()
File "/Applications/GoogleAppEngineLauncher.app/Contents/Resources/GoogleAppEngine-default.bundle/Contents/Resources/google_appengine/google/appengine/tools/devappserver2/devappserver2.py", line 865, in main
dev_server.start(options)
File "/Applications/GoogleAppEngineLauncher.app/Contents/Resources/GoogleAppEngine-default.bundle/Contents/Resources/google_appengine/google/appengine/tools/devappserver2/devappserver2.py", line 692, in start
apis.start()
File "/Applications/GoogleAppEngineLauncher.app/Contents/Resources/GoogleAppEngine-default.bundle/Contents/Resources/google_appengine/google/appengine/tools/devappserver2/api_server.py", line 137, in start
super(APIServer, self).start()
File "/Applications/GoogleAppEngineLauncher.app/Contents/Resources/GoogleAppEngine-default.bundle/Contents/Resources/google_appengine/google/appengine/tools/devappserver2/wsgi_server.py", line 317, in start
raise BindError('Unable to find a consistent port for %s' % host)
google.appengine.tools.devappserver2.wsgi_server.BindError: Unable to find a consistent port for localhost
但奇怪的是我确实安装了PIL。我知道这是因为（a）我安装了它，（b）GAE确实启动了一段时间。
可能是什么问题？