Are you using this pugin in a Multisite WP?. I had similar problem and was because I’m using a multisite WordPress and I’ve activated the plugin in network plugins instead the site plugins. I’ve disabled the plugin into network plugins and I’ve activated it just for the site and the error disappeared.
How to Get Support
After you register and login to the site, you may post all plugin support questions in the Support Forum.
If you need to provide private info, please create a ticket and then reply to it using Set as private reply option.