This is preventing widgets from loading.
I think the issue is related to events with invitees who are not thread members.
2015/06/15 13:55:39 [error] 14488#0: *1477 FastCGI sent in stderr: "PHP message: [2015-06-15 13:55:39] ERROR 8: Undefined index: PHID-USER-n5twvd2a4ms3k7clhfd7 at [/core/lib/phabricator/src/applications/conpherence/controller/ConpherenceWidgetController.php:314] PHP message: arcanist(head=master, ref.master=fe4856277c6c), phabricator(head=master, ref.master=069568757242), phutil(head=master, ref.master=3b4da3f33153) PHP message: #0 ConpherenceWidgetController::renderCalendarWidgetPaneContent() called at [<phabricator>/src/applications/conpherence/controller/ConpherenceWidgetController.php:108] PHP message: #1 ConpherenceWidgetController::renderWidgetPaneContent() called at [<phabricator>/src/applications/conpherence/controller/ConpherenceWidgetController.php:55] PHP message: #2 ConpherenceWidgetController::handleRequest(AphrontRequest) called at [<phabricator>/src/aphront/configuration/AphrontApplicationConfiguration.php:226] PHP message: #3 AphrontApplicationConfiguration::processRequest(AphrontRequest, PhutilDeferredLog, AphrontPHPHTTPSink, MultimeterControl) called at [<phabricator>/src/aphront/configuration/AphrontApplicationConfiguration.php:140] PHP message: #4 AphrontApplicationConfiguration::runHTTPRequest(AphrontPHPHTTPSink) called at [<phabricator>/webroot/index.php:21]
PHP message: >>> UNRECOVERABLE FATAL ERROR <<< Call to a member function getName() on a non-object /core/lib/phabricator/src/applications/conpherence/controller/ConpherenceWidgetController.php:314 ┻━┻ ︵ ¯\_(ツ)_/¯ ︵ ┻━┻"