I made a 2.0 plugin in installed-plugins inaccessable (no permissions) to JIRA and restarted. I got this and a lovely 404 error:

java.lang.RuntimeException: Could not open JAR file for reading: e:\blitz\home\plugins\installed-plugins\jira-toolkit-0.7.29-SNAPSHOT.jar
	at com.atlassian.plugin.JarPluginArtifact.getInputStream(JarPluginArtifact.java:106)
	at com.atlassian.plugin.factories.XmlDynamicPluginFactory.canCreate(XmlDynamicPluginFactory.java:123)
	at com.atlassian.plugin.loaders.ScanningPluginLoader.deployPluginFromUnit(ScanningPluginLoader.java:111)
	at com.atlassian.plugin.loaders.ScanningPluginLoader.loadAllPlugins(ScanningPluginLoader.java:87)
	at com.atlassian.plugin.manager.DefaultPluginManager.init(DefaultPluginManager.java:150)
	at com.atlassian.jira.plugin.JiraPluginManager.start(JiraPluginManager.java:49)
	at com.atlassian.jira.ComponentManager$PluginSystem.start(ComponentManager.java:1276)
	at com.atlassian.jira.ComponentManager.quickStart(ComponentManager.java:200)
	at com.atlassian.jira.ComponentManager.start(ComponentManager.java:186)
	at com.atlassian.jira.upgrade.ConsistencyLauncher.launchConsistencyChecker(ConsistencyLauncher.java:59)
	at com.atlassian.jira.upgrade.ConsistencyLauncher.contextInitialized(ConsistencyLauncher.java:40)
	at org.apache.catalina.core.StandardContext.listenerStart(StandardContext.java:3764)
	at org.apache.catalina.core.StandardContext.start(StandardContext.java:4216)
	at org.apache.catalina.core.ContainerBase.start(ContainerBase.java:1014)
	at org.apache.catalina.core.StandardHost.start(StandardHost.java:736)
	at org.apache.catalina.core.ContainerBase.start(ContainerBase.java:1014)
	at org.apache.catalina.core.StandardEngine.start(StandardEngine.java:443)
	at org.apache.catalina.core.StandardService.start(StandardService.java:448)
	at org.apache.catalina.core.StandardServer.start(StandardServer.java:700)
	at org.apache.catalina.startup.Catalina.start(Catalina.java:552)
	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 org.apache.catalina.startup.Bootstrap.start(Bootstrap.java:295)
	at org.apache.catalina.startup.Bootstrap.main(Bootstrap.java:433)
Caused by: java.io.FileNotFoundException: e:\blitz\home\plugins\installed-plugins\jira-toolkit-0.7.29-SNAPSHOT.jar (Access is denied)
	at java.io.FileInputStream.open(Native Method)
	at java.io.FileInputStream.<init>(FileInputStream.java:106)
	at com.atlassian.plugin.JarPluginArtifact.getInputStream(JarPluginArtifact.java:102)
	... 25 more
2009-06-11 19:42:53,970 Main Thread INFO [atlassian.plugin.manager.DefaultPluginManager] Plugin system started in 0:00:15.734
2009-06-11 19:42:53,970 Main Thread ERROR [com.atlassian.jira.ComponentManager] Error occurred while starting PluginManager.
com.atlassian.jira.util.dbc.Assertions$NullArgumentException: name should not be null!
	at com.atlassian.jira.util.dbc.Assertions.notNull(Assertions.java:24)
	at com.atlassian.jira.util.dbc.Null.not(Null.java:12)
	at com.atlassian.jira.plugin.PluginVersionImpl.<init>(PluginVersionImpl.java:31)
	at com.atlassian.jira.plugin.JiraPluginManager.storePluginVersion(JiraPluginManager.java:155)
	at com.atlassian.jira.plugin.JiraPluginManager.storePluginVersions(JiraPluginManager.java:130)
	at com.atlassian.jira.plugin.JiraPluginManager.start(JiraPluginManager.java:50)
	at com.atlassian.jira.ComponentManager$PluginSystem.start(ComponentManager.java:1276)
	at com.atlassian.jira.ComponentManager.quickStart(ComponentManager.java:200)
	at com.atlassian.jira.ComponentManager.start(ComponentManager.java:186)
	at com.atlassian.jira.upgrade.ConsistencyLauncher.launchConsistencyChecker(ConsistencyLauncher.java:59)
	at com.atlassian.jira.upgrade.ConsistencyLauncher.contextInitialized(ConsistencyLauncher.java:40)
	at org.apache.catalina.core.StandardContext.listenerStart(StandardContext.java:3764)
	at org.apache.catalina.core.StandardContext.start(StandardContext.java:4216)
	at org.apache.catalina.core.ContainerBase.start(ContainerBase.java:1014)
	at org.apache.catalina.core.StandardHost.start(StandardHost.java:736)
	at org.apache.catalina.core.ContainerBase.start(ContainerBase.java:1014)
	at org.apache.catalina.core.StandardEngine.start(StandardEngine.java:443)
	at org.apache.catalina.core.StandardService.start(StandardService.java:448)
	at org.apache.catalina.core.StandardServer.start(StandardServer.java:700)
	at org.apache.catalina.startup.Catalina.start(Catalina.java:552)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
	at java.lang.reflect.Method.invoke(Method.java:597)
	at org.apache.catalina.startup.Bootstrap.start(Bootstrap.java:295)
	at org.apache.catalina.startup.Bootstrap.main(Bootstrap.java:433)
2009-06-11 19:42:53,986 Main Thread FATAL [atlassian.jira.upgrade.ConsistencyLauncher] A RuntimeException occurred during ConsistencyLauncher servlet context initialisation - Error occurred while starting PluginManager..
com.atlassian.jira.InfrastructureException: Error occurred while starting PluginManager.
	at com.atlassian.jira.ComponentManager$PluginSystem.start(ComponentManager.java:1281)
	at com.atlassian.jira.ComponentManager.quickStart(ComponentManager.java:200)
	at com.atlassian.jira.ComponentManager.start(ComponentManager.java:186)
	at com.atlassian.jira.upgrade.ConsistencyLauncher.launchConsistencyChecker(ConsistencyLauncher.java:59)
	at com.atlassian.jira.upgrade.ConsistencyLauncher.contextInitialized(ConsistencyLauncher.java:40)
	at org.apache.catalina.core.StandardContext.listenerStart(StandardContext.java:3764)
	at org.apache.catalina.core.StandardContext.start(StandardContext.java:4216)
	at org.apache.catalina.core.ContainerBase.start(ContainerBase.java:1014)
	at org.apache.catalina.core.StandardHost.start(StandardHost.java:736)
	at org.apache.catalina.core.ContainerBase.start(ContainerBase.java:1014)
	at org.apache.catalina.core.StandardEngine.start(StandardEngine.java:443)
	at org.apache.catalina.core.StandardService.start(StandardService.java:448)
	at org.apache.catalina.core.StandardServer.start(StandardServer.java:700)
	at org.apache.catalina.startup.Catalina.start(Catalina.java:552)
	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 org.apache.catalina.startup.Bootstrap.start(Bootstrap.java:295)
	at org.apache.catalina.startup.Bootstrap.main(Bootstrap.java:433)
Caused by: com.atlassian.jira.util.dbc.Assertions$NullArgumentException: name should not be null!
	at com.atlassian.jira.util.dbc.Assertions.notNull(Assertions.java:24)
	at com.atlassian.jira.util.dbc.Null.not(Null.java:12)
	at com.atlassian.jira.plugin.PluginVersionImpl.<init>(PluginVersionImpl.java:31)
	at com.atlassian.jira.plugin.JiraPluginManager.storePluginVersion(JiraPluginManager.java:155)
	at com.atlassian.jira.plugin.JiraPluginManager.storePluginVersions(JiraPluginManager.java:130)
	at com.atlassian.jira.plugin.JiraPluginManager.start(JiraPluginManager.java:50)
	at com.atlassian.jira.ComponentManager$PluginSystem.start(ComponentManager.java:1276)