RPC plugin fails to start because of duplicate plugin key

JIRA-3.6.4 Professional WAR/EAR (Evaluation). Modified edit-webapp/entityengine.xml to comply with my appserver/database, and built with "build ear".

When trying to access /jira/rpc/soap/jirasoapservice-v2?wsdl I get : "HTTP Status 503 - Remote API not activated for this JIRA installation.".

In the appserver log it prints:
[#|2006-09-02T00:19:58.687+0300|INFO|sun-appserver-ee9.1|javax.enterprise.system.stream.out|_ThreadID=10;_ThreadName=main;|2006-09-02 00:19:58,671 WARN [atlassian.jira.plugin.JiraPluginManager] Failed to parse plugin
com.atlassian.plugin.PluginParseException: Duplicate plugin key found: 'com.atlassian.jira.ext.rpc'
at com.atlassian.plugin.DefaultPluginManager.addPlugin(DefaultPluginManager.java:118)
at com.atlassian.jira.plugin.JiraPluginManager.addPlugin(JiraPluginManager.java:129)
at com.atlassian.plugin.DefaultPluginManager.init(DefaultPluginManager.java:49)
at com.atlassian.jira.plugin.JiraPluginManager.start(JiraPluginManager.java:44)
at com.atlassian.jira.ComponentManager.quickStart(ComponentManager.java:273)
at com.atlassian.jira.ComponentManager.start(ComponentManager.java:254)
at com.atlassian.jira.upgrade.ConsistencyLauncher.contextInitialized(ConsistencyLauncher.java:25)
at org.apache.catalina.core.StandardContext.listenerStart(StandardContext.java:4236)
at org.apache.catalina.core.StandardContext.start(StandardContext.java:4760)
at com.sun.enterprise.web.WebModule.start(WebModule.java:292)
at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:833)
at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:817)
at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:662)
at com.sun.enterprise.web.WebContainer.loadWebModule(WebContainer.java:1495)
at com.sun.enterprise.web.WebContainer.loadWebModule(WebContainer.java:1160)
at com.sun.enterprise.web.WebContainer.loadJ2EEApplicationWebModules(WebContainer.java:1085)
at com.sun.enterprise.server.TomcatApplicationLoader.load(TomcatApplicationLoader.java:128)
at com.sun.enterprise.server.AbstractManager.load(AbstractManager.java:206)
at com.sun.enterprise.server.ApplicationLifecycle.onStartup(ApplicationLifecycle.java:204)
at com.sun.enterprise.server.ApplicationServer.onStartup(ApplicationServer.java:326)
at com.sun.enterprise.server.ondemand.OnDemandServer.onStartup(OnDemandServer.java:112)
at com.sun.enterprise.server.PEMain.run(PEMain.java:326)
at com.sun.enterprise.server.PEMain.main(PEMain.java:260)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at com.sun.enterprise.server.PELaunch.main(PELaunch.java:272)