Hi Angela,
Thanks for reaching out, and I’m so sorry for the trouble here! This error message can sometimes occur when a license key for one of our other products, such as Events Calendar PRO, is entered into the license key field for Event Aggregator. Please ensure that you’ve installed the Events Calendar PRO plugin alongside the free version of The Events Calendar and entered your license key into the field that appears for Events Calendar PRO after installing and activating the plugin. You can find directions for setting up Events Calendar PRO on our New User Primer here on our Knowledgebase.
I hope that helps to get you started here! Thanks again for your support, and please don’t hesitate to follow up if there’s anything else that we can assist with!