just tested this. I get the same error but, only in firefox. after hitting ok this Assertion failure error text is shown
Assertion failure: A plugin is missing. Check the plugin IDs match in edittime and runtime scripts. Note this can also occur when there is an error in a plugin script that prevents the browser from loading the script - check the error console.
Stack trace:
assert2@http://10.0.0.2:50000/preview_prelude.js:16:10
Runtime.prototype.loadProject@http://10.0.0.2:50000/preview.js:1173:4
Runtime.prototype.requestProjectData/xhr.onload@http://10.0.0.2:50000/preview.js:396:6