When I try to install a plugin in Eclipse I get these error messages

Registry event dispatcher

Error notifying registry change listener.
Error notifying registry change listener.
Invalid registry object
Error notifying registry change listener.
Invalid registry object
Error notifying registry change listener.
Invalid registry object
Error notifying registry change listener.
Invalid registry object
Error notifying registry change listener.
Invalid registry object

Has someone an idea what the cause of this problem could be? Thanks

Edit:

I see the Eclipse .log file has also a lot of new stack traces

The first one is

java.vendor=Sun Microsystems Inc.
BootLoader constants: OS=win32, ARCH=x86_64, WS=win32, NL=nl_NL
Framework arguments:  -product org.eclipse.epp.package.jee.product
Command-line arguments:  -os win32 -ws win32 -arch x86_64 -product org.eclipse.epp.package.jee.product

!ENTRY org.eclipse.equinox.registry 4 2 2010-05-06 21:04:31.236
!MESSAGE Problems occurred when invoking code from plug-in: "org.eclipse.equinox.registry".
!STACK 0
org.eclipse.core.runtime.InvalidRegistryObjectException: Invalid registry object
    at org.eclipse.core.internal.registry.TemporaryObjectManager.getObject(TemporaryObjectManager.java:98)
    at org.eclipse.core.internal.registry.BaseExtensionPointHandle.getExtensionPoint(BaseExtensionPointHandle.java:106)
    at org.eclipse.core.internal.registry.BaseExtensionPointHandle.getContributor(BaseExtensionPointHandle.java:45)
    at org.eclipse.core.internal.registry.BaseExtensionPointHandle.getNamespace(BaseExtensionPointHandle.java:37)
    at org.eclipse.ui.internal.PopupMenuExtender.registryChanged(PopupMenuExtender.java:520)
    at org.eclipse.core.internal.registry.ExtensionRegistry$2.run(ExtensionRegistry.java:921)
    at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:42)
    at org.eclipse.core.internal.registry.ExtensionRegistry.processChangeEvent(ExtensionRegistry.java:919)
    at org.eclipse.core.runtime.spi.RegistryStrategy.processChangeEvent(RegistryStrategy.java:260)
    at org.eclipse.core.internal.registry.osgi.ExtensionEventDispatcherJob.run(ExtensionEventDispatcherJob.java:50)
    at org.eclipse.core.internal.jobs.Worker.run(Worker.java:54)