Cannot open .bp or .bpml file with Graphical Process Modeler

Symptom

When the file is opened a the filename displays in the titlebar.

No icons are displayed and the View Source is not available.

This does not happen with all files.

Exception visible in the Java console:

Exception in thread "AWT-EventQueue-0" java.lang.NoClassDefFoundError: com/sterlingcommerce/woodstock/util/BaseUtil
at com.sterlingcommerce.woodstock.gbm.common.lang.bpml.v0_3.base.FlowParser.parseFl ow(FlowParser.java:127)
at com.sterlingcommerce.woodstock.gbm.common.lang.bpml.v0_3.FlowParserWrapper.parse Process(FlowParserWrapper.java:93)
at com.sterlingcommerce.woodstock.gbm.editor.lang.bpml.v0_3.LangFileReader.readLang File(LangFileReader.java:80)
at com.sterlingcommerce.woodstock.gbm.common.ui.jgo.FlowDocument.handleLangFile(Flo wDocument.java:866)
at com.sterlingcommerce.woodstock.gbm.common.ui.jgo.FlowDocument.open(FlowDocument. java:818)
at com.sterlingcommerce.woodstock.gbm.editor.jgo.FlowBuilderMain.openFlow(FlowBuild erMain.java:1187)
at com.sterlingcommerce.woodstock.gbm.editor.jgo.FlowBuilderMain.openFlow(FlowBuild erMain.java:1112)
at com.sterlingcommerce.woodstock.gbm.editor.jgo.BuildMenu.actionPerformed(BuildMen u.java:1380)
at com.sterlingcommerce.woodstock.gbm.editor.jgo.actions.FlowAbstractAction.actionP erformed(FlowAbstractAction.java:171)
at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
at javax.swing.DefaultButtonModel.setPressed(Unknown Source)
at javax.swing.AbstractButton.doClick(Unknown Source)
at javax.swing.plaf.basic.BasicMenuItemUI.doClick(Unknown Source)
at javax.swing.plaf.basic.BasicMenuItemUI$Handler.mouseReleased(Unknown Source)
at java.awt.AWTEventMulticaster.mouseReleased(Unknown Source)
at java.awt.AWTEventMulticaster.mouseReleased(Unknown Source)
at java.awt.Component.processMouseEvent(Unknown Source)
at javax.swing.JComponent.processMouseEvent(Unknown Source)
at java.awt.Component.processEvent(Unknown Source)
at java.awt.Container.processEvent(Unknown Source)
at java.awt.Component.dispatchEventImpl(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Window.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.EventQueue.dispatchEvent(Unknown Source)
at java.awt.EventDispatchThread.pumpOneEventForHierarchy(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)