@alina n
It looks like that you need to add value “localhost” or "127.0.0.1" for parameter hadoop.proxyuser.oozie.hosts in /etc/hadoop/conf/core-site.xml. Once you add this through ambari-ui, please save and restart the Oozie service.
<property>
<name>hadoop.proxyuser.oozie.hosts</name>
<value>127.0.0.1,localhost,sandbox.hortonworks.com</value>
</property>
Hope this helps you.