Hey,
The following two properties are required in Hadoop core-site.xml:
<property>
<name>hadoop.proxyuser.[OOZIE_SERVER_USER].hosts</name>
<value>[OOZIE_SERVER_HOSTNAME]</value>
</property>
<property>
<name>hadoop.proxyuser.[OOZIE_SERVER_USER].groups</name>
<value>[USER_GROUPS_THAT_ALLOW_IMPERSONATION]</value>
</property>
Replace the capital letter sections with specific values and then restart Hadoop.