Hello, sorry for the issues.
I can help you get to the bottom of this and make that message go away.
I took a look at your site and it looks like The Events Calendar and The Events Calendar Pro are both using the latest version.
Step 1
So, the first thing I would try is deactivating both plugins,then active them to see if the message goes away.
Step 2
If that does not work try deactivating both plugins, deleting both and re-uploading the latest version and then activating them again to see if it the message goes away.
Step 3
If that does not solve the problem can you try out Testing for Conflicts Guide and let me know if that removes the message.
https://theeventscalendar.com/support/documentation/testing-for-conflicts/
Also if the message is still there, can you tell me the exact page it is appearing on. You only need to send the url.
Please let me know what you find out and we can go from there.
Thanks