There is a «Please wait» sign that doesn’t go away after installing a Mage2.PRO extension to Magento 2.0.x

Hmmm, I still can’t enable the plugin cause of js errors. There is please wait sign that doesn’t go away… can you please check why is this happening?

Yes, I have reproduced it and will fix it now.
Do not do anything with the website.

I have fixed the JavaScript issues: