Omeka has encountered an error

Exception

String could not be parsed as XML

exception 'Exception' with message 'String could not be parsed as XML' in /home/evivliothiki/public_html/plugins/SocialBookmarking/helpers/SocialBookmarkingFunctions.php:45
Stack trace:
#0 /home/evivliothiki/public_html/plugins/SocialBookmarking/helpers/SocialBookmarkingFunctions.php(45): SimpleXMLElement->__construct('')
#1 /home/evivliothiki/public_html/plugins/SocialBookmarking/helpers/SocialBookmarkingFunctions.php(55): social_bookmarking_get_services_xml()
#2 /home/evivliothiki/public_html/plugins/SocialBookmarking/helpers/SocialBookmarkingFunctions.php(85): social_bookmarking_get_services()
#3 /home/evivliothiki/public_html/plugins/SocialBookmarking/SocialBookmarkingPlugin.php(136): social_bookmarking_toolbar('http://evivliot...', 'Open courses\r\n\xCE...', '\xCE\xA4\xCE\xB9 \xCE\xB5\xCE\xAF\xCE\xBD\xCE\xB1\xCE\xB9...')
#4 [internal function]: SocialBookmarkingPlugin->hookPublicItemsShow(Array)
#5 /home/evivliothiki/public_html/application/libraries/Omeka/Plugin/Broker.php(157): call_user_func(Array, Array)
#6 /home/evivliothiki/public_html/application/libraries/globals.php(188): Omeka_Plugin_Broker->callHook('public_items_sh...', Array)
#7 /home/evivliothiki/public_html/themes/seasons/items/show.php(13): fire_plugin_hook('public_items_sh...', Array)
#8 /home/evivliothiki/public_html/application/libraries/Omeka/View.php(117): include('/home/evivlioth...')
#9 /home/evivliothiki/public_html/application/libraries/Zend/View/Abstract.php(888): Omeka_View->_run('/home/evivlioth...')
#10 /home/evivliothiki/public_html/application/libraries/Zend/Controller/Action/Helper/ViewRenderer.php(912): Zend_View_Abstract->render('items/show.php')
#11 /home/evivliothiki/public_html/application/libraries/Zend/Controller/Action/Helper/ViewRenderer.php(933): Zend_Controller_Action_Helper_ViewRenderer->renderScript('items/show.php', NULL)
#12 /home/evivliothiki/public_html/application/libraries/Zend/Controller/Action/Helper/ViewRenderer.php(972): Zend_Controller_Action_Helper_ViewRenderer->render()
#13 /home/evivliothiki/public_html/application/libraries/Zend/Controller/Action/HelperBroker.php(277): Zend_Controller_Action_Helper_ViewRenderer->postDispatch()
#14 /home/evivliothiki/public_html/application/libraries/Zend/Controller/Action.php(527): Zend_Controller_Action_HelperBroker->notifyPostDispatch()
#15 /home/evivliothiki/public_html/application/libraries/Zend/Controller/Dispatcher/Standard.php(308): Zend_Controller_Action->dispatch('showAction')
#16 /home/evivliothiki/public_html/application/libraries/Zend/Controller/Front.php(954): Zend_Controller_Dispatcher_Standard->dispatch(Object(Zend_Controller_Request_Http), Object(Zend_Controller_Response_Http))
#17 /home/evivliothiki/public_html/application/libraries/Zend/Application/Bootstrap/Bootstrap.php(105): Zend_Controller_Front->dispatch()
#18 /home/evivliothiki/public_html/application/libraries/Zend/Application.php(384): Zend_Application_Bootstrap_Bootstrap->run()
#19 /home/evivliothiki/public_html/application/libraries/Omeka/Application.php(79): Zend_Application->run()
#20 /home/evivliothiki/public_html/index.php(23): Omeka_Application->run()
#21 {main}