Facebook graph api returns photo link that expires after some period

I'm using facebook graph api to get page cover url. I'm using the query like GET /v2.3/{page-id}. It returns structure like:

{...
    "cover": {...
        "source": "https://fbcdn-sphotos-b-a.akamaihd.net/..."
    }
...
}

Recently I have discovered that this link returned error: "An error occurred while processing your request. Reference #50.1d0adfad.1428868729.19b3c7d5." What does this error mean? Did anybody get the same error?

The link: https://fbcdn-sphotos-b-a.akamaihd.net/hphotos-ak-xpa1/v/t1.0-9/s720x720/1004859_section.10152218387031749_948700280_n.jpg?oh=cb66f8cd74647137cafcd8b305567c14&oe=54C00B8E&gda=1421781046_ba46001e1912f7bd322627bc5592a6f1