Can't start Elasticsearch (fileInputStream Fail) - elasticsearch

Question

I'm currently building up a test environment for HPE ALM Octane for my company. This Application uses Elasticsearch. Now I have the problem, that I can't start my Elasticsearchserver and I'm a bit at the end of my nerves ;).
Cause Octane works with Elasticsearch version 2.4.0, I'm also forced to work with this version.
I get the following Error:
Error - Console Screenshot
elasticsearch.service - Elasticsearch
Loaded: loaded (/usr/lib/systemd/system/elasticsearch.service;
enabled; vendor preset: disabled)
Active: failed (Result: exit-code) since Tue 2017-02-21 09:40:50 CET; 1h 9min ago
Process: 954 ExecStart=/usr/share/elasticsearch/bin/elasticsearch
-Des.pidfile=${PID_DIR}/elasticsearch.pid
-Des.default.path.home=${ES_HOME} -Des.default.path.logs=${LOG_DIR}
-Des.default.path.data=${DATA_DIR} -Des.default.path.conf=${CONF_DIR}
(code=exited, status=1/FAILURE)
Process: 949 ExecStartPre=/usr/share/elasticsearch/bin/elasticsearch-systemd-pre-exec (code=exited, status=0/SUCCESS)
Main PID: 954 (code=exited, status=1/FAILURE)
Feb 21 09:40:50 linux-rfw5 elasticsearch[954]: at java.nio.file.Files.newInputStream(Files.java:152)
Feb 21 09:40:50 linux-rfw5 elasticsearch[954]: at org.elasticsearch.common.settings.Settings$Builder.loadFromPath(Settings.java:1067)
Feb 21 09:40:50 linux-rfw5 elasticsearch[954]: at org.elasticsearch.node.internal.InternalSettingsPreparer.prepareEnvironment(InternalSettingsPreparer.java:88)
Feb 21 09:40:50 linux-rfw5 elasticsearch[954]: at org.elasticsearch.bootstrap.Bootstrap.initialSettings(Bootstrap.java:218)
Feb 21 09:40:50 linux-rfw5 elasticsearch[954]: at org.elasticsearch.bootstrap.Bootstrap.init(Bootstrap.java:257)
Feb 21 09:40:50 linux-rfw5 elasticsearch[954]: at org.elasticsearch.bootstrap.Elasticsearch.main(Elasticsearch.java:35)
Feb 21 09:40:50 linux-rfw5 elasticsearch[954]: Refer to the log for complete error details.
Feb 21 09:40:50 linux-rfw5 systemd 1 : elasticsearch.service: Main process exited, code=exited, status=1/FAILURE
Feb 21 09:40:50 linux-rfw5 systemd 1 : elasticsearch.service: Unit entered failed state.
Feb 21 09:40:50 linux-rfw5 systemd 1 : elasticsearch.service: Failed with result 'exit-code'.
I configured the absolute minimum, that is possible. My Configurations:
elasticsearch.yml (/etc/elasticsearch/)
1.1 cluster.name: octane_test
1.2 node.name: elasticNode
1.3 network.host: 127.0.0.1 (yes localhost, cause I'm running the octane server on the same host)
http.port: 9200 elasticsearch (/etc/sysconfig/)
2.1 ES_HEAP_SIZE=4g (4 GB is 50% of the maximum memory)
I appreciate your help ;)
Joel