Plugin seems to be broken, it says it has no write access to the /wp-config.php - but in fact it has!
The Dev Staging Environment plugin is not installed correctly. Please ensure the web server has read and write access to the /wp-config.php file and click here to reinstall the plugin
Also in the config dialog in HOST text box this is printed:
<b>Warning</b>: implode() [function.implode]: Invalid arguments passed in <b>/DATA/WORDPRESS/wp_sandbox/wp-content/plugins/dev-and-staging-environment/dev-staging-plugin.php</b> on line <b>160</b>
More over there is no additional hint what to do or how to use this plugin. I will test more, but seems like an update is neccessary anyway...