Problem while installing Marvel

Could any of you help me with this error I am getting:
./bin/plugin install elasticsearch/marvel/latest

Stack trace of errror:
Exception in thread "main" java.lang.IllegalArgumentException: Could not resolve placeholder 'ES_RACK'
at org.elasticsearch.common.settings.ImmutableSettings$Builder.replacePropertyPlaceholders(
at org.elasticsearch.node.internal.InternalSettingsPreparer.prepareSettings(
at org.elasticsearch.plugins.PluginManager.main(

I must agree that ES_RACK is an environment variable I am setting in a file called setenv and not in elasticsearch.yml.
How do I come over this error?

What version of ES you have?

It's 1.4.4.