A somewhat rare but highly annoying error...
Line 28 in the jphoto content plugin:
$menu = &JSite::getMenu();
causes errors with some components which invoke onPrepareContent from the backend (JXtended Finder, K2).
FIX:
This line seems deprecated (its the only reference to $menu) so it can be removed. In generally JFactory::getApplication() is preferred to JSite...