Cannot read property 'string' of undefined
when i'm import the module ( import { Button } from 'react-lightning-design-system'; ) i got the error on my browser window "Cannot read property 'string' of undefined". even i am not using it.
( But I found that it is working with react v15.6.1 )

Yes, because PropTypes were deprecated in React 15.5 and removed in React 16. #238 should fix that problem.
Still happening in v2.4.5. There are still references to React.PropTypes here:
https://github.com/mashmatrix/react-lightning-design-system/blob/6e1f587b5492faa233f537937ba08a132bde3d66/src/scripts/Table.js#L167
and here: https://github.com/mashmatrix/react-lightning-design-system/blob/1e80f8784933ebc7fdc21b9421570e305eb7d23c/stories/GridStories.js#L16
Not sure if master has been pushed to NPM yet.