This error means we have not been able to retrieve the given list, playlist, album, artist or song correctly.
It could be because the given list or URL is not well-formed/incorrect, or it could be because the given destination API (developer access) does not allow developers to access such a resource.
For example, Spotify does not allow developers to export or transfer playlists made by Spotify to another service or as a backup (see Spotify Developer Policy here).
We must fully comply with these Spotify Developer Policies, which is also true for other APIs we use.