There are a few situations that may cause the following message to pop-up in your screen:
Where does this message show, and what is it caused by?
This message is related to the web gallery. This will show when accessing the public gallery link for an event or a specific file link.
There are certain reasons that cause this:
Deleted event. When an event is deleted, so is the gallery, so the public gallery can no longer be accessed.
Expired event. Similarly to the deleted events, expired events have their galleries erased after the indicated expiration date.
Disable webgallery access. This is an option that hides the web gallery from the website, making it appear as if it does not exist. This option should be disabled for you or guests to see the web gallery. This setting location is: Event Manager / Web Gallery Branding / Security.