Openstrap and charts plugins

I love your theme but encountered a problem with plugins that should visualize data in different kinds of charts (pie, bar, etc.).

I have already tried Easychart Builder and WordPress Charts but after inserting the shortcode for a chart into a post it doesn’t appear as it should. Instead of the chart you merely see a grey box without content.

Do you have any idea how to deal with this? I don’t think it’s a plugin-related issue since I run Easychart Builder on another site using another theme without any problems (also, I deactivated all the plugins that I don’t have installed on the other site – no change).

http://www.ehnur21.at (the respective site, however, is currently saved as a draft)