With clean profile and clean new dev build I installed all available plugins (more than 100) and after restart I got the
following exception:

java.lang.ClassNotFoundException: org.netbeans.modules.j2ee.websphere6.ddloaders.appext.WSAppExtDataObject
	at java.net.URLClassLoader$1.run(URLClassLoader.java:200)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.net.URLClassLoader.findClass(URLClassLoader.java:188)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
	at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:268)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:251)
	at org.netbeans.ProxyClassLoader.loadClass(ProxyClassLoader.java:231)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:251)
	at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:319)
	at java.lang.Class.forName0(Native Method)
	at java.lang.Class.forName(Class.java:242)
	at org.openide.loaders.DataLoader.getRepresentationClass(DataLoader.java:141)
Caused: java.lang.IllegalStateException: Failed to load
org.netbeans.modules.j2ee.websphere6.ddloaders.appext.WSAppExtDataObject from
org.netbeans.StandardModule$OneModuleClassLoader@1179c1c[org.netbeans.modules.j2ee.websphere6]
	at org.openide.loaders.DataLoader.getRepresentationClass(DataLoader.java:143)
	at org.openide.loaders.DataLoader.<init>(DataLoader.java:125)
	at org.openide.loaders.MultiFileLoader.<init>(MultiFileLoader.java:77)
	at org.openide.loaders.UniFileLoader.<init>(UniFileLoader.java:79)
	at org.netbeans.modules.j2ee.websphere6.dd.loaders.appext.WSAppExtDataLoader.<init>(WSAppExtDataLoader.java:35)
Caused: java.lang.reflect.InvocationTargetException
	at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
	at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39)
	at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)
	at java.lang.reflect.Constructor.newInstance(Constructor.java:494)
	at org.openide.util.SharedClassObject.createInstancePrivileged(SharedClassObject.java:641)
	at org.openide.util.SharedClassObject$SetAccessibleAction.run(SharedClassObject.java:1001)
	at org.openide.util.SharedClassObject$SetAccessibleAction.run(SharedClassObject.java:993)
	at java.security.AccessController.doPrivileged(Native Method)
	at org.openide.util.SharedClassObject.findObject(SharedClassObject.java:515)
Caused: java.lang.IllegalArgumentException
	at org.openide.util.SharedClassObject.findObject(SharedClassObject.java:518)
	at org.netbeans.core.startup.ManifestSection.createInstance(ManifestSection.java:198)
	at org.netbeans.core.startup.ManifestSection.getInstance(ManifestSection.java:216)
	at org.netbeans.core.LoaderPoolNode.add(LoaderPoolNode.java:204)
	at org.netbeans.core.CoreBridgeImpl.loadLoaderSection(CoreBridgeImpl.java:95)
	at org.netbeans.core.startup.NbInstaller.loadSections(NbInstaller.java:432)
	at org.netbeans.core.startup.NbInstaller.load(NbInstaller.java:271)
	at org.netbeans.ModuleManager.enable(ModuleManager.java:933)
	at org.netbeans.core.startup.ModuleList.installNew(ModuleList.java:405)
	at org.netbeans.core.startup.ModuleList.trigger(ModuleList.java:341)
	at org.netbeans.core.startup.ModuleSystem.restore(ModuleSystem.java:275)
	at org.netbeans.core.startup.Main.getModuleSystem(Main.java:171)
	at org.netbeans.core.startup.Main.start(Main.java:322)
	at org.netbeans.core.startup.TopThreadGroup.run(TopThreadGroup.java:110)
[catch] at java.lang.Thread.run(Thread.java:595)


Product Version: NetBeans IDE Dev (Build 200711150000)
Java: 1.5.0_13; Java HotSpot(TM) Client VM 1.5.0_13-b05
System: Windows XP version 5.1 running on x86; Cp1250; pl_PL (nb)