Hello Joan,
I can fix the error on your site, if you provide me FTP details. Otherwise you need wait for the upcoming update of the plugin, it will be released in a week or two.
Or you can fix it by yourself. Follow these instructions:
1) Open this file ow_plugins/questions/classes/newsfeed_bridge.php
2) Find this code in the file:
$language = OW::getLanguage();
$configs = OW::getConfig()->getValues('questions');
$questionId = $params['action']['entityId'];
3) Replace it with this code:
$language = OW::getLanguage();
$configs = OW::getConfig()->getValues('questions');
$questionId = $params['action']['entityId'];
$userId = OW::getUser()->getId(); // This line fixes the error