Couldn't find index page for 'PasteScript'

在 Plone 4.0.2 正常運作一段時間後，因為修改 src 目錄裡的自製模組，需要重新執行 bin/buildout，遇到錯誤訊息：

Download error: (-2, 'Name or service not known') -- Some packages may not be found!
Couldn't find index page for 'PasteScript' (maybe misspelled?)

distutils.errors.DistutilsError:
 Could not find suitable distribution for Requirement.parse('PasteScript')
While:
  Installing.
  Processing develop directory '/home/marr/mysite/zinstance/src/my.package'.

檢查 my.package/setup.py 裡面有一行 setup_requires=["PasteScript"], 設定值，註解掉暫時有排除問題，但仍不清楚原理。
另外在 Problems running Buildout to install a them created with Paster 有類似的討論，或許會有正確解答的線索。