appian engines dont start after appian upgrade to 18.4

Hi all,

We see the below error after upgrading to appian 18.4

[bpm@blbbpmsappt01 bin]$ ./start.sh -p appian -s all
Starting Distributed Transaction Log
Executing command: '[null/bin/java, -Xms128m, -Xmx256m, -Dzookeeper.log.dir=/appdata/appian/logs/service-manager/zookeeper, -Dzookeeper.root.logger=INFO,CONSOLE,ROLLINGFILE, -Duser.timezone=GMT, -cp, /appdata/appian/services/zookeeper-3.4.11/zookeeper-3.4.11.jar:/appdata/appian/services/zookeeper-3.4.11/lib/slf4j-log4j12-1.6.1.jar:/appdata/appian/services/zookeeper-3.4.11/lib/slf4j-api-1.6.1.jar:/appdata/appian/services/zookeeper-3.4.11/lib/netty-3.10.5.Final.jar:/appdata/appian/services/zookeeper-3.4.11/lib/log4j-1.2.16.jar:/appdata/appian/services/zookeeper-3.4.11/lib/jline-0.9.94.jar:/appdata/appian/services/zookeeper-3.4.11/lib/audience-annotations-0.5.0.jar:/appdata/appian/services/zookeeper-3.4.11/conf, org.apache.zookeeper.server.quorum.QuorumPeerMain, /appdata/appian/services/conf/zookeeper.properties]' in /appdata/appian/services/zookeeper-3.4.11/bin with environment [:]
Unable to start service QuorumPeerMain

Any idea why?