Thread:Project:Support desk/Fatal error: cannot access private property/reply (11)

-> https://github.com/kulttuuri/hipchat_mediawiki/blob/master/HipchatNotifications/hipchat_notifications.php#L165

It's Hipchat extension. It tries to get the description of an uploaded image/file via LocalFile (which is private). Can you try to remove the extension and try again?