Custom field in Magpie code

Warning: MagpieRSS: Failed to fetch /home/path/to/my/install/plugins/pi.magpie.php on line 1386

Notice: Trying to get property of non-object in /home/path/to/my/install/plugins/pi.magpie.php on line 105

{exp:magpie url="{center_events_feed}" limit="10" refresh="720" feed_type="atom"}
<ul>
{magpie:items}
<li><a href="http://{magpie:link}">{magpie:title}</a></li>
{/magpie:items}
</ul>
{/exp:magpie}