Sorry about that. Looks like we left an out-of-date dependency in the package manifest. The module thinks it needs the AjaxControlToolkit, but we removed that early on in development. If you feel comfortable, you can alter EngageEvents.dnn in the zip file, then package it all up, and try to reinstall it.
You will need to remove line 11 in EngageEvents.dnn, where it says "<dependencies>AjaxControlToolkit.PopupControlExtender; AjaxControlToolkit.ToolkitScriptManager</dependencies>"
Again, sorry for your inconvenience.