 <p>If anyone hit the problem again: <a href="https://forums.activiti.org/content/activiti-explorer-runs-return-error#comment-35300" rel="nofollow">https://forums.activiti.org/content/activiti-explorer-runs-return-error#comment-35300</a></p> <p>A possible solution is to set a servlet filter in the web.xml file to add a header X-UA-Compatible to the http response. An alternative remedy would be to upgrage Vaadin to 6.8 version according to this post <a href="https://dev.vaadin.com/ticket/12635" rel="nofollow">https://dev.vaadin.com/ticket/12635</a>.</p>