The upgrade of your Enforce server may have removed the springSecurityContext.xml file required to enable Active Directory authentication. If the springSecurityContext.xml file is present, check the contents of the file, around lines 95-102 and see if this is missing:
<!-- Set krbConfLocation in System properties -->
C:\SymantecDLP\Protect\config\krb5.ini
<bean class="org.springframework.security.kerberos.authentication.sun.GlobalSunJaasKerberosConfig">
<!-- krb5 configuration file location.
For exampleon Windows or /opt/Vontu/Protect/config/krb5.conf on Linux
-->
<property name="krbConfLocation" value="C:\SymantecDLP\Protect\config\krb5.ini" />
</bean>
To restore functionality:
On your enforce sever, here is the location of the backup file: "\SymantecDLP\Protect\updates\SymantecDLPEnforceBackup\SymantecDLPEnforceBackup_15.0.0.45028\Protect\tomcat\webapps\ProtectManager\WEB-INF\springSecurityContext.xml"
If the springSecurityContext.xml needs to be replaced, rename the current file version, then copy the good backup .xml file here: \SymantecDLP\Protect\tomcat\webapps\ProtectManager\WEB-INF\springSecurityContext.xml
With the backup in place, restart the VontuManager service. Active Directory functionality will be restored.