Omeka has encountered an error

Exception

DateTime::__construct(): Failed to parse time string (936?/01/01) at position 0 (9): Unexpected character

exception 'Exception' with message 'DateTime::__construct(): Failed to parse time string (936?/01/01) at position 0 (9): Unexpected character' in /sites/repphlit/www/web_main/themes/phlit/custom.php:673
Stack trace:
#0 /sites/repphlit/www/web_main/themes/phlit/custom.php(673): DateTime->__construct('936?/01/01')
#1 [internal function]: phlit_item_is_older_than(Object(Item), Object(Item))
#2 /sites/repphlit/www/web_main/themes/phlit/items/show-ecrivain.php(61): usort(Array, 'phlit_item_is_o...')
#3 /sites/repphlit/www/web_main/themes/phlit/items/show.php(9): include('/sites/repphlit...')
#4 /sites/repphlit/www/web_main/application/libraries/Omeka/View.php(117): include('/sites/repphlit...')
#5 /sites/repphlit/www/web_main/application/libraries/Zend/View/Abstract.php(888): Omeka_View->_run('/sites/repphlit...')
#6 /sites/repphlit/www/web_main/application/libraries/Zend/Controller/Action/Helper/ViewRenderer.php(912): Zend_View_Abstract->render('items/show.php')
#7 /sites/repphlit/www/web_main/application/libraries/Zend/Controller/Action/Helper/ViewRenderer.php(933): Zend_Controller_Action_Helper_ViewRenderer->renderScript('items/show.php', NULL)
#8 /sites/repphlit/www/web_main/application/libraries/Zend/Controller/Action/Helper/ViewRenderer.php(972): Zend_Controller_Action_Helper_ViewRenderer->render()
#9 /sites/repphlit/www/web_main/application/libraries/Zend/Controller/Action/HelperBroker.php(277): Zend_Controller_Action_Helper_ViewRenderer->postDispatch()
#10 /sites/repphlit/www/web_main/application/libraries/Zend/Controller/Action.php(527): Zend_Controller_Action_HelperBroker->notifyPostDispatch()
#11 /sites/repphlit/www/web_main/application/libraries/Zend/Controller/Dispatcher/Standard.php(308): Zend_Controller_Action->dispatch('showAction')
#12 /sites/repphlit/www/web_main/application/libraries/Zend/Controller/Front.php(954): Zend_Controller_Dispatcher_Standard->dispatch(Object(Zend_Controller_Request_Http), Object(Zend_Controller_Response_Http))
#13 /sites/repphlit/www/web_main/application/libraries/Zend/Application/Bootstrap/Bootstrap.php(105): Zend_Controller_Front->dispatch()
#14 /sites/repphlit/www/web_main/application/libraries/Zend/Application.php(384): Zend_Application_Bootstrap_Bootstrap->run()
#15 /sites/repphlit/www/web_main/application/libraries/Omeka/Application.php(77): Zend_Application->run()
#16 /sites/repphlit/www/web_main/index.php(23): Omeka_Application->run()
#17 {main}