Error Message "Internal error: Unable to open model."

Hi, I am using ARIS 9.0 and trying to open a model and for some reason when I do, I get the message "Internal error: Unable to open model." And the details provided are as follows: 

Thu Jan 30 13:02:47 AST 2014: Internal error: Unable to open model. com.aris.modeling.common.core.ADebug.Assert(ADebug.java:47) com.aris.modeling.common.core.ADebug.Assert(ADebug.java:33) com.aris.modeling.common.core.arisdesignerbase.corearisobjects.logic.AUnionHelper.getChildren(AUnionHelper.java:138) com.aris.modeling.common.core.arisdesignerbase.corearisobjects.logic.AUnionHelper.getChildren(AUnionHelper.java:125) com.aris.modeling.common.serverremoteapi.cscommon.corearisdesigner.logic.hasunion.ARecursiveEmbeddingRepairer.checkChildren(ARecursiveEmbeddingRepairer.java:36) com.aris.modeling.common.serverremoteapi.cscommon.corearisdesigner.logic.hasunion.ARecursiveEmbeddingRepairer.checkChildren(ARecursiveEmbeddingRepairer.java:41) com.aris.modeling.common.serverremoteapi.cscommon.corearisdesigner.logic.hasunion.ARecursiveEmbeddingRepairer.repairRecursiveEmbeddings(ARecursiveEmbeddingRepairer.java:27) com.aris.modeling.client.components.basecomponents.corearisdesigner.om.logic.openmodel.ACoreModelOpenHandler.repairRecursiveEmbeddings(ACoreModelOpenHandler.java:152) com.aris.modeling.client.components.basecomponents.corearisdesigner.om.logic.openmodel.ACoreModelOpenHandler.applyCheckPoint(ACoreModelOpenHandler.java:106) com.aris.modeling.client.components.basecomponents.corearisdesigner.om.logic.openmodel.ACoreModelOpenHandler.createAModel(ACoreModelOpenHandler.java:90) com.aris.modeling.client.components.basecomponents.webdesignerbase.arisobjects.logic.model.openmodel.AOpenModel.openModel(AOpenModel.java:100) com.aris.modeling.client.components.basecomponents.webdesignerbase.arisobjects.logic.model.AModelLogicHelper.openModelInternal(AModelLogicHelper.java:351) com.aris.modeling.client.components.basecomponents.webdesignerbase.logic.ADesignerOpenService.openNode(ADesignerOpenService.java:133) com.aris.modeling.client.framework.services.AAbstractOpenService.openNode(AAbstractOpenService.java:47) com.aris.modeling.client.framework.aris.AFrameworkServiceHelper.openAllNodesOfActionContext(AFrameworkServiceHelper.java:119) com.aris.modeling.client.container.controller.ACommandController.openWithOpenHandler(ACommandController.java:52) com.aris.modeling.client.container.controller.ACommandController.openNode(ACommandController.java:33) com.aris.modeling.client.container.common.AContainerHelper.openModel(AContainerHelper.java:48) com.aris.modeling.client.container.common.AContainerHelper.openModel(AContainerHelper.java:40) com.aris.modeling.client.components.explorer.ArisOpenNodeEventHandler.execute(ArisOpenNodeEventHandler.java:94) com.aris.modeling.client.components.explorer.ArisOpenNodeEventHandler.execute(ArisOpenNodeEventHandler.java:35) com.aris.modeling.client.common.explorer.core.controller.ExplorerEventManager.processEvent(ExplorerEventManager.java:27) com.aris.modeling.client.common.explorer.core.tree.BaseExplorerTreeComponent.openNodeEvent(BaseExplorerTreeComponent.java:780) com.aris.modeling.client.common.explorer.core.controller.BaseExplorerEnvironmentController.openNodeEvent(BaseExplorerEnvironmentController.java:47) com.aris.modeling.client.common.explorer.core.controller.BaseExplorerEnvironmentController.sendEvent(BaseExplorerEnvironmentController.java:42) com.softwareag.aris.client.explorer.view.swing.base.tree.interaction.DefaultExplorerTreeOpenNodeInteraction.mouseClicked(DefaultExplorerTreeOpenNodeInteraction.java:67) com.softwareag.aris.client.explorer.view.swing.base.common.controllers.DefaultSwingInteractionController.dispatchMouseEvent(DefaultSwingInteractionController.java:487) com.softwareag.aris.client.explorer.view.swing.base.common.controllers.DefaultSwingInteractionController.dispatchEvent(DefaultSwingInteractionController.java:464) com.softwareag.aris.client.explorer.view.swing.base.common.controllers.DefaultSwingInteractionController.handleEvent(DefaultSwingInteractionController.java:391) com.softwareag.aris.client.explorer.view.swing.base.common.controllers.DefaultSwingInteractionController.handleMouseEvent(DefaultSwingInteractionController.java:408) com.softwareag.aris.client.explorer.view.swing.base.common.controllers.DefaultSwingInteractionController.mousePressed(DefaultSwingInteractionController.java:252) java.awt.AWTEventMulticaster.mousePressed(AWTEventMulticaster.java:280) java.awt.AWTEventMulticaster.mousePressed(AWTEventMulticaster.java:279) java.awt.AWTEventMulticaster.mousePressed(AWTEventMulticaster.java:279) java.awt.Component.processMouseEvent(Component.java:6502) javax.swing.JComponent.processMouseEvent(JComponent.java:3321) com.softwareag.aris.client.explorer.view.swing.impl.tree.treecontrol.SwingTreeControlImpl.processMouseEvent(SwingTreeControlImpl.java:409) java.awt.Component.processEvent(Component.java:6270) java.awt.Container.processEvent(Container.java:2229) java.awt.Component.dispatchEventImpl(Component.java:4861) java.awt.Container.dispatchEventImpl(Container.java:2287) java.awt.Component.dispatchEvent(Component.java:4687) java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4832) java.awt.LightweightDispatcher.processMouseEvent(Container.java:4489) java.awt.LightweightDispatcher.dispatchEvent(Container.java:4422) java.awt.Container.dispatchEventImpl(Container.java:2273) java.awt.Window.dispatchEventImpl(Window.java:2719) java.awt.Component.dispatchEvent(Component.java:4687) java.awt.EventQueue.dispatchEventImpl(EventQueue.java:729) java.awt.EventQueue.access$200(EventQueue.java:103) java.awt.EventQueue$3.run(EventQueue.java:688) java.awt.EventQueue$3.run(EventQueue.java:686) java.security.AccessController.doPrivileged(Native Method) java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76) java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:87) java.awt.EventQueue$4.run(EventQueue.java:702) java.awt.EventQueue$4.run(EventQueue.java:700) java.security.AccessController.doPrivileged(Native Method) java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76) java.awt.EventQueue.dispatchEvent(EventQueue.java:699) com.aris.modeling.client.container.common.AFocusManager.dispatchEvent(AFocusManager.java:124) java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:242) java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:161) java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:150) java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:146) java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:138) java.awt.EventDispatchThread.run(EventDispatchThread.java:91)

I appreciate your help. Regards, Tariq