Yes, logged in as super user. Can't create categories and hence can't create events. This is a brand new site with not much on it as I'm still adding pages and menu items as I have time. I've tried uninstalling and reinstalling the jem event package and even upgraded it to the 2.2.1 today and still no dice. On event or category, I get no error messages, you can't cancel or anything, you have to hit back to get out of it.
I can't reproduce your issue:
I made a fresh and clean install of joomla 3.7.1 and JEM 2.2.1 (multilingual) on php 7.1.3. (no other plugins, modules and templates. I am using the protostar template.
I am in backend as superuser and create first a category. Then I create an event.
There are no problems!
It seems you have installed some additional things which interferes with Joomla and JEM. So I will be sure you will encounter more problems not only in JEM.
Perhaps it helps, if you consult the help in backend!
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