Data retrieval failure error message:

java.lang.Exception: org.openmicroscopy.shoola.env.data.DSAccessException: Cannot access data.
Cannot load hierarchy for class pojos.DatasetData.
     at org.openmicroscopy.shoola.env.data.OMEROGateway.handleException(OMEROGateway.java:896)
     at org.openmicroscopy.shoola.env.data.OMEROGateway.loadContainerHierarchy(OMEROGateway.java:2641)
     at org.openmicroscopy.shoola.env.data.OmeroDataServiceImpl.loadContainerHierarchy(OmeroDataServiceImpl.java:221)
     at org.openmicroscopy.shoola.env.data.views.calls.DMLoader$1.doCall(DMLoader.java:91)
     at org.openmicroscopy.shoola.env.data.views.BatchCall.doStep(BatchCall.java:144)
     at org.openmicroscopy.shoola.util.concur.tasks.CompositeTask.doStep(CompositeTask.java:226)
     at org.openmicroscopy.shoola.env.data.views.CompositeBatchCall.doStep(CompositeBatchCall.java:126)
     at org.openmicroscopy.shoola.util.concur.tasks.ExecCommand.exec(ExecCommand.java:165)
     at org.openmicroscopy.shoola.util.concur.tasks.ExecCommand.run(ExecCommand.java:276)
     at org.openmicroscopy.shoola.util.concur.tasks.AsyncProcessor$Runner.run(AsyncProcessor.java:91)
     at java.lang.Thread.run(Unknown Source)
Caused by: Ice.DNSException
    error = 0
    host = "gretzky.openmicroscopy.org.uk"
     at IceInternal.Network.getAddresses(Network.java:867)
     at IceInternal.EndpointHostResolver.run(EndpointHostResolver.java:94)
     at IceInternal.EndpointHostResolver$HelperThread.run(EndpointHostResolver.java:146)
Caused by: java.net.UnknownHostException: gretzky.openmicroscopy.org.uk
     at java.net.Inet6AddressImpl.lookupAllHostAddr(Native Method)
     at java.net.InetAddress$1.lookupAllHostAddr(Unknown Source)
     at java.net.InetAddress.getAddressFromNameService(Unknown Source)
     at java.net.InetAddress.getAllByName0(Unknown Source)
     at java.net.InetAddress.getAllByName(Unknown Source)
     at java.net.InetAddress.getAllByName(Unknown Source)
     at IceInternal.Network.getAddresses(Network.java:854)
     ... 2 more

     at org.openmicroscopy.shoola.env.ui.UserNotifierImpl.showErrorDialog(UserNotifierImpl.java:189)
     at org.openmicroscopy.shoola.env.ui.UserNotifierImpl.notifyError(UserNotifierImpl.java:287)
     at org.openmicroscopy.shoola.env.ui.UserNotifierImpl.notifyError(UserNotifierImpl.java:257)
     at org.openmicroscopy.shoola.agents.treeviewer.DataBrowserLoader.handleException(DataBrowserLoader.java:148)
     at org.openmicroscopy.shoola.env.data.events.DSCallAdapter.eventFired(DSCallAdapter.java:84)
     at org.openmicroscopy.shoola.env.data.views.BatchCallMonitor$1.run(BatchCallMonitor.java:124)
     at java.awt.event.InvocationEvent.dispatch(Unknown Source)
     at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
     at java.awt.EventQueue.access$400(Unknown Source)
     at java.awt.EventQueue$2.run(Unknown Source)
     at java.awt.EventQueue$2.run(Unknown Source)
     at java.security.AccessController.doPrivileged(Native Method)
     at java.security.AccessControlContext$1.doIntersectionPrivilege(Unknown Source)
     at java.awt.EventQueue.dispatchEvent(Unknown Source)
     at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
     at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
     at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
     at java.awt.Dialog$1.run(Unknown Source)
     at java.awt.Dialog$3.run(Unknown Source)
     at java.security.AccessController.doPrivileged(Native Method)
     at java.awt.Dialog.show(Unknown Source)
     at java.awt.Component.show(Unknown Source)
     at java.awt.Component.setVisible(Unknown Source)
     at java.awt.Window.setVisible(Unknown Source)
     at java.awt.Dialog.setVisible(Unknown Source)
     at org.openmicroscopy.shoola.util.ui.UIUtilities.centerAndShow(UIUtilities.java:558)
     at org.openmicroscopy.shoola.env.ui.UserNotifierImpl.showErrorDialog(UserNotifierImpl.java:197)
     at org.openmicroscopy.shoola.env.ui.UserNotifierImpl.notifyError(UserNotifierImpl.java:287)
     at org.openmicroscopy.shoola.env.ui.UserNotifierImpl.notifyError(UserNotifierImpl.java:257)
     at org.openmicroscopy.shoola.agents.metadata.MetadataLoader.handleException(MetadataLoader.java:164)
     at org.openmicroscopy.shoola.env.data.events.DSCallAdapter.eventFired(DSCallAdapter.java:84)
     at org.openmicroscopy.shoola.env.data.views.BatchCallMonitor$1.run(BatchCallMonitor.java:124)
     at java.awt.event.InvocationEvent.dispatch(Unknown Source)
     at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
     at java.awt.EventQueue.access$400(Unknown Source)
     at java.awt.EventQueue$2.run(Unknown Source)
     at java.awt.EventQueue$2.run(Unknown Source)
     at java.security.AccessController.doPrivileged(Native Method)
     at java.security.AccessControlContext$1.doIntersectionPrivilege(Unknown Source)
     at java.awt.EventQueue.dispatchEvent(Unknown Source)
     at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
     at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
     at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
     at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
     at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
     at java.awt.EventDispatchThread.run(Unknown Source)