Ooops, sorry, I have found the ICS file and I think that I have reproduced the importer issue.
So, the importer actually shows a small “Error” label in the bottom-left corner and the log contains this:
java.lang.NoClassDefFoundError: org/apache/commons/codec/DecoderException
at net.fortuna.ical4j.model.PropertyFactoryImpl$AttachFactory.createProperty(PropertyFactoryImpl.java:196)
at net.fortuna.ical4j.model.PropertyFactoryImpl.createProperty(PropertyFactoryImpl.java:972)
at net.fortuna.ical4j.data.CalendarBuilder$ContentHandlerImpl.startProperty(CalendarBuilder.java:346)
at net.fortuna.ical4j.data.CalendarParserImpl$PropertyParser.parse(CalendarParserImpl.java:211)
at net.fortuna.ical4j.data.CalendarParserImpl$PropertyParser.access$1(CalendarParserImpl.java:200)
at net.fortuna.ical4j.data.CalendarParserImpl$PropertyListParser.parse(CalendarParserImpl.java:178)
at net.fortuna.ical4j.data.CalendarParserImpl$ComponentParser.parse(CalendarParserImpl.java:396)
at net.fortuna.ical4j.data.CalendarParserImpl$ComponentParser.access$1(CalendarParserImpl.java:382)
at net.fortuna.ical4j.data.CalendarParserImpl$PropertyListParser.parse(CalendarParserImpl.java:175)
at net.fortuna.ical4j.data.CalendarParserImpl$ComponentParser.parse(CalendarParserImpl.java:396)
at net.fortuna.ical4j.data.CalendarParserImpl$ComponentParser.access$1(CalendarParserImpl.java:382)
at net.fortuna.ical4j.data.CalendarParserImpl$PropertyListParser.parse(CalendarParserImpl.java:175)
at net.fortuna.ical4j.data.CalendarParserImpl.parse(CalendarParserImpl.java:125)
at net.fortuna.ical4j.data.CalendarBuilder.build(CalendarBuilder.java:210)
at biz.ganttproject.impex.ical.IcsFileImporter.readEvents(IcsFileImporter.java:152)
at biz.ganttproject.impex.ical.IcsFileImporter.setFile(IcsFileImporter.java:101)
at net.sourceforge.ganttproject.importer.FileChooserPage.setFile(FileChooserPage.java:74)
at net.sourceforge.ganttproject.wizard.AbstractFileChooserPage.onSelectedFileChange(AbstractFileChooserPage.java:288)
at net.sourceforge.ganttproject.wizard.AbstractFileChooserPage.loadPreferences(AbstractFileChooserPage.java:202)
at net.sourceforge.ganttproject.wizard.AbstractFileChooserPage.setActive(AbstractFileChooserPage.java:228)
at net.sourceforge.ganttproject.wizard.AbstractWizard.nextPage(AbstractWizard.java:111)
at net.sourceforge.ganttproject.wizard.AbstractWizard.access$000(AbstractWizard.java:42)
at net.sourceforge.ganttproject.wizard.AbstractWizard$1.actionPerformed(AbstractWizard.java:77)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2022)
at javax.swing.AbstractButton$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:6539)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3324)
at java.awt.Component.processEvent(Component.java:6304)
at java.awt.Container.processEvent(Container.java:2239)
at java.awt.Component.dispatchEventImpl(Component.java:4889)
at java.awt.Container.dispatchEventImpl(Container.java:2297)
at java.awt.Component.dispatchEvent(Component.java:4711)
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4904)
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4535)
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4476)
at java.awt.Container.dispatchEventImpl(Container.java:2283)
at java.awt.Window.dispatchEventImpl(Window.java:2746)
at java.awt.Component.dispatchEvent(Component.java:4711)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:760)
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:74)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:84)
at java.awt.EventQueue$4.run(EventQueue.java:733)
at java.awt.EventQueue$4.run(EventQueue.java:731)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:74)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:730)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:205)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:109)
at java.awt.WaitDispatchSupport$2.run(WaitDispatchSupport.java:190)
at java.awt.WaitDispatchSupport$4.run(WaitDispatchSupport.java:235)
at java.awt.WaitDispatchSupport$4.run(WaitDispatchSupport.java:233)
at java.security.AccessController.doPrivileged(Native Method)
at java.awt.WaitDispatchSupport.enter(WaitDispatchSupport.java:233)
at java.awt.Dialog.show(Dialog.java:1084)
at java.awt.Component.show(Component.java:1671)
at java.awt.Component.setVisible(Component.java:1623)
at java.awt.Window.setVisible(Window.java:1014)
at java.awt.Dialog.setVisible(Dialog.java:1005)
at net.sourceforge.ganttproject.DialogBuilder$DialogImpl.show(DialogBuilder.java:148)
at net.sourceforge.ganttproject.wizard.AbstractWizard.show(AbstractWizard.java:151)
at net.sourceforge.ganttproject.action.project.ProjectImportAction.actionPerformed(ProjectImportAction.java:50)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2022)
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2348)
at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:402)
at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259)
at javax.swing.AbstractButton.doClick(AbstractButton.java:376)
at javax.swing.plaf.basic.BasicMenuItemUI.doClick(BasicMenuItemUI.java:842)
at javax.swing.plaf.basic.BasicMenuItemUI$Handler.mouseReleased(BasicMenuItemUI.java:886)
at java.awt.Component.processMouseEvent(Component.java:6539)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3324)
at java.awt.Component.processEvent(Component.java:6304)
at java.awt.Container.processEvent(Container.java:2239)
at java.awt.Component.dispatchEventImpl(Component.java:4889)
at java.awt.Container.dispatchEventImpl(Container.java:2297)
at java.awt.Component.dispatchEvent(Component.java:4711)
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4904)
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4535)
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4476)
at java.awt.Container.dispatchEventImpl(Container.java:2283)
at java.awt.Window.dispatchEventImpl(Window.java:2746)
at java.awt.Component.dispatchEvent(Component.java:4711)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:760)
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:74)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:84)
at java.awt.EventQueue$4.run(EventQueue.java:733)
at java.awt.EventQueue$4.run(EventQueue.java:731)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:74)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:730)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:205)
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)
Caused by: java.lang.ClassNotFoundException: org.apache.commons.codec.DecoderException
at java.net.URLClassLoader.findClass(URLClassLoader.java:382)
at org.bardsoftware.impl.eclipsito.BundleClassLoader.findClass(BundleClassLoader.java:131)
at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
... 108 more
This issue seems to be fixed in the beta of GanttProject 3.0, and I highly encourage to try it. You can download the latest build 2.99.2906 from here: https://www.dropbox.com/sh/ijzr7s7ozxqexls/AADlRUGq667XQjEK8j4StEp2a?dl=0
The ICS imports fine in GP 2.99.2906. It adds a number of holidays to the project calendar. You can check it in Project > Properties > Calendar