I'm not sure if is awesomium settings for C2 exporter. According to this support forum 1.7 supports Drag and Drop files. http://support.awesomium.com/discussions/problems/275-does-awesomium-v161-support-the-html5-drag-and-drop-draggable-attribute
I've used this plugin
http://www.scirra.com/FORUM/topic58578.html and it worked very fine, then exported to Awesomium, it seems drag and drop is disabled.
I'm afraid we can't support third party plugins, so closing. Contact the developer for help with the plugin.
FYI Awesomium is still based on Chrome 18, so it's possible it's still not supported.
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It has nothing to do with 3rd party plugin, it's about API for HTML5, i noticed some thread in Awesomium forum, they say Awesomium is a windowless, they cannot support drag and drop files. Anyway, thanks.