You get this error:

Error: Events is currently unavailable.
DotNetNuke.Services.Exceptions.ModuleLoadException: Object reference not set to an instance of an object. ---> System.NullReferenceException: Object reference not set to an instance of an object. at DotNetNuke.Modules.Events.SelectCategory.get_SelectedCategory() at DotNetNuke.Modules.Events.EventList.BindDataGrid() at DotNetNuke.Modules.Events.EventList.Page_Load(Object sender, EventArgs e) --- End of inner exception stack trace ---

Go to:

 [Module] > Settings > Event Module Settings and check the "Disable Category Select" option and click Apply.