Using toolbox version 3.0.0-20160118 on Mac OSX 10.11.2, with 14.5GB Ram allocated to SNAP and the following two products, although this problem is not product specific:
S1A_IW_SLC__1SDV_20150312T162305_20150312T162339_005001_006448_E5A3.zip
S1A_IW_SLC__1SDV_20150324T162306_20150324T162339_005176_006871_C040.zip
When running the S1 TOPS Coregistration graph, after selecting an external dem for back-geocoding a NullPointerException is raised:
java.lang.NullPointerException at org.esa.snap.dem.dataio.DEMFactory.getDEMDisplayName(DEMFactory.java:119) at org.esa.s1tbx.sentinel1.gpf.ui.BackGeocodingOpUI.initParameters(BackGeocodingOpUI.java:132) at org.esa.snap.graphbuilder.gpf.ui.BaseOperatorUI.setSourceProducts(BaseOperatorUI.java:107) at org.esa.snap.graphbuilder.rcp.dialogs.support.GraphNode.setSourceProducts(GraphNode.java:338) at org.esa.snap.graphbuilder.rcp.dialogs.support.GraphNodeList.updateGraphNodes(GraphNodeList.java:97) at org.esa.snap.graphbuilder.rcp.dialogs.support.GraphExecuter.InitGraph(GraphExecuter.java:253) at org.esa.snap.graphbuilder.rcp.dialogs.GraphBuilderDialog.InitGraph(GraphBuilderDialog.java:325) at org.esa.snap.graphbuilder.rcp.dialogs.GraphBuilderDialog.ValidateAllNodes(GraphBuilderDialog.java:532) at org.esa.snap.graphbuilder.rcp.dialogs.GraphBuilderDialog.DoProcessing(GraphBuilderDialog.java:283) at org.esa.snap.graphbuilder.rcp.dialogs.GraphBuilderDialog$3.actionPerformed(GraphBuilderDialog.java:223) at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2022) at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2348) at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:402) at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259) at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:252) at java.awt.AWTEventMulticaster.mouseReleased(AWTEventMulticaster.java:289) at java.awt.Component.processMouseEvent(Component.java:6535) at javax.swing.JComponent.processMouseEvent(JComponent.java:3324) at java.awt.Component.processEvent(Component.java:6300) at java.awt.Container.processEvent(Container.java:2236) at java.awt.Component.dispatchEventImpl(Component.java:4891) at java.awt.Container.dispatchEventImpl(Container.java:2294) at java.awt.Component.dispatchEvent(Component.java:4713) at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4888) at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4525) at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4466) at java.awt.Container.dispatchEventImpl(Container.java:2280) at java.awt.Window.dispatchEventImpl(Window.java:2750) at java.awt.Component.dispatchEvent(Component.java:4713) at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:758) at java.awt.EventQueue.access$500(EventQueue.java:97) at java.awt.EventQueue$3.run(EventQueue.java:709) at java.awt.EventQueue$3.run(EventQueue.java:703) at java.security.AccessController.doPrivileged(Native Method) at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:76) at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:86) at java.awt.EventQueue$4.run(EventQueue.java:731) at java.awt.EventQueue$4.run(EventQueue.java:729) at java.security.AccessController.doPrivileged(Native Method) at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:76) at java.awt.EventQueue.dispatchEvent(EventQueue.java:728) at org.netbeans.core.TimableEventQueue.dispatchEvent(TimableEventQueue.java:159) at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:201) at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116) at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:105) at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101) at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93) at java.awt.EventDispatchThread.run(EventDispatchThread.java:82)