Upgrade does not work

We are trying to upgrade from (Enterprise Edition, Version: 3.0.3-#75) to (Enterprise Edition, Version: 3.1)

This does not work, and the following can be found in the log:

—
2005-05-25 10:50:48 StandardContext[]: Exception sending context initialized event to listener instance of class com.atlassian.jira.upgrade.ConsistencyLaun
cher
com.atlassian.plugin.PluginParseException: Duplicate plugin key found: 'com.atlassian.jira.ext.rpc'
        at com.atlassian.plugin.DefaultPluginManager.addPlugin(DefaultPluginManager.java:42)
        at com.atlassian.plugin.DefaultPluginManager.init(DefaultPluginManager.java:33)
        at com.atlassian.jira.plugin.JiraPluginManager.start(JiraPluginManager.java:39)
        at com.atlassian.jira.ComponentManager.quickStart(ComponentManager.java:225)
        at com.atlassian.jira.ComponentManager.start(ComponentManager.java:206)
        at com.atlassian.jira.upgrade.ConsistencyLauncher.contextInitialized(ConsistencyLauncher.java:25)
        at org.apache.catalina.core.StandardContext.listenerStart(StandardContext.java:3271)
        at org.apache.catalina.core.StandardContext.start(StandardContext.java:3613)
        at org.apache.catalina.core.ContainerBase.start(ContainerBase.java:1188)
        at org.apache.catalina.core.StandardHost.start(StandardHost.java:754)
        at org.apache.catalina.core.ContainerBase.start(ContainerBase.java:1188)
        at org.apache.catalina.core.StandardEngine.start(StandardEngine.java:363)
        at org.apache.catalina.core.StandardService.start(StandardService.java:497)
        at org.apache.catalina.core.StandardServer.start(StandardServer.java:2190)
        at org.apache.catalina.startup.Catalina.start(Catalina.java:512)
        at org.apache.catalina.startup.Catalina.execute(Catalina.java:400)
        at org.apache.catalina.startup.Catalina.process(Catalina.java:180)
        at java.lang.reflect.Method.invoke(Native Method)
        at org.apache.catalina.startup.Bootstrap.main(Bootstrap.java:203)
rethrown as com.atlassian.jira.InfrastructureException: Error occurred while starting component.: Duplicate plugin key found: 'com.atlassian.jira.ext.rpc'
        at com.atlassian.jira.ComponentManager.quickStart(ComponentManager.java:230)
        at com.atlassian.jira.ComponentManager.start(ComponentManager.java:206)
        at com.atlassian.jira.upgrade.ConsistencyLauncher.contextInitialized(ConsistencyLauncher.java:25)
        at org.apache.catalina.core.StandardContext.listenerStart(StandardContext.java:3271)
        at org.apache.catalina.core.StandardContext.start(StandardContext.java:3613)
        at org.apache.catalina.core.ContainerBase.start(ContainerBase.java:1188)
        at org.apache.catalina.core.StandardHost.start(StandardHost.java:754)
        at org.apache.catalina.core.ContainerBase.start(ContainerBase.java:1188)
        at org.apache.catalina.core.StandardEngine.start(StandardEngine.java:363)
        at org.apache.catalina.core.StandardService.start(StandardService.java:497)
        at org.apache.catalina.core.StandardServer.start(StandardServer.java:2190)
        at org.apache.catalina.startup.Catalina.start(Catalina.java:512)
        at org.apache.catalina.startup.Catalina.execute(Catalina.java:400)
        at org.apache.catalina.startup.Catalina.process(Catalina.java:180)
        at java.lang.reflect.Method.invoke(Native Method)
        at org.apache.catalina.startup.Bootstrap.main(Bootstrap.java:203)
2005-05-25 10:50:48 StandardContext[]: Context startup failed due to previous errors