not sure how I got it but I got this error:

java.util.ConcurrentModificationException
at java.util.ArrayList$Itr.checkForComodification(ArrayList.java:819)
at java.util.ArrayList$Itr.next(ArrayList.java:791)
at org.jboss.tools.central.internal.discovery.wizards.ProxyWizardManager.notifyListeners(ProxyWizardManager.java:260)
at org.jboss.tools.central.internal.discovery.wizards.ProxyWizardManager.loadWizards(ProxyWizardManager.java:105)
at org.jboss.tools.central.internal.discovery.wizards.ProxyWizardUpdateJob.run(ProxyWizardUpdateJob.java:44)
at org.eclipse.core.internal.jobs.Worker.run(Worker.java:53)

I think I had closed and reopened central again but not sure - the error took some seconds before it showed up.