Error in using three graphs for 'mean' operation?

I loaded 3 bams, got depth graphs, zoomed in, select these three graphs asked for a 'mean' and got the following error.

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at com.affymetrix.igb.view.SeqMapView.setToolTip(SeqMapView.java:2343)
at com.affymetrix.igb.view.SeqMapView.setShowPropertiesTooltip(SeqMapView.java:2417)
at com.affymetrix.igb.action.ToggleToolTipAction.actionPerformed(ToggleToolTipAction.java:46)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2018)
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2341)
at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:402)
at javax.swing.JToggleButton$ToggleButtonModel.setPressed(JToggleButton.java:308)
at javax.swing.AbstractButton.doClick(AbstractButton.java:376)
at com.apple.laf.ScreenMenuItemCheckbox.itemStateChanged(ScreenMenuItemCheckbox.java:196)
at java.awt.CheckboxMenuItem.processItemEvent(CheckboxMenuItem.java:389)
at java.awt.CheckboxMenuItem.processEvent(CheckboxMenuItem.java:357)
at java.awt.MenuComponent.dispatchEventImpl(MenuComponent.java:351)
at java.awt.MenuComponent.dispatchEvent(MenuComponent.java:339)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:732)
at java.awt.EventQueue.access$200(EventQueue.java:103)
at java.awt.EventQueue$3.run(EventQueue.java:688)
at java.awt.EventQueue$3.run(EventQueue.java:686)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:87)
at java.awt.EventQueue$4.run(EventQueue.java:702)
at java.awt.EventQueue$4.run(EventQueue.java:700)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:699)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:242)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:161)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:150)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:146)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:138)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:91)
java.lang.NullPointerException
at com.affymetrix.genometryImpl.style.GraphState.getHeatMap(GraphState.java:162)
at com.affymetrix.genometryImpl.operator.AbstractGraphOperator.operate(AbstractGraphOperator.java:181)
at com.affymetrix.genometryImpl.symloader.Delegate.getRegion(Delegate.java:105)
at com.affymetrix.genometryImpl.quickload.QuickLoadSymLoader.loadAndAddSymmetries(QuickLoadSymLoader.java:155)
at com.affymetrix.genometryImpl.quickload.QuickLoadSymLoader.loadSymmetriesThread(QuickLoadSymLoader.java:129)
at com.affymetrix.genometryImpl.quickload.QuickLoadSymLoader.loadFeatures(QuickLoadSymLoader.java:109)
at com.affymetrix.genometryImpl.symloader.Delegate.loadFeatures(Delegate.java:180)
at com.affymetrix.genometryImpl.util.LocalFilesServerType.loadFeatures(LocalFilesServerType.java:101)
at com.affymetrix.igb.view.load.GeneralLoadUtils.loadFeaturesForSym(GeneralLoadUtils.java:846)
at com.affymetrix.igb.view.load.GeneralLoadUtils$3.runInBackground(GeneralLoadUtils.java:786)
at com.affymetrix.igb.view.load.GeneralLoadUtils$3.runInBackground(GeneralLoadUtils.java:781)
at com.affymetrix.genometryImpl.thread.CThreadWorker.doInBackground(CThreadWorker.java:61)
at javax.swing.SwingWorker$1.call(SwingWorker.java:296)
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:334)
at java.util.concurrent.FutureTask.run(FutureTask.java:166)
at javax.swing.SwingWorker.run(SwingWorker.java:335)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
at java.lang.Thread.run(Thread.java:722)