gluon: project wizard could not be started at eclipse 2018-12

Question

The wizard for creating a gluon-project with the gluon-plugin (Version 2.6.0) cannot be started.

error message:

The selected wizard could not be started. Plug-in com.gluonhq.eclipse.plugin was unable to load class com.gluonhq.eclipse.plugin.wizard.desktop.singleview.GluonProjectSingleApplicationWizard. An error occurred while automatically activating bundle com.gluonhq.eclipse.plugin (1259).

entry in the .log file:

!ENTRY org.eclipse.equinox.registry 4 1 2019-01-14 17:25:32.846
!MESSAGE Plug-in com.gluonhq.eclipse.plugin was unable to load class com.gluonhq.eclipse.plugin.menu.ValidationSourceProvider.
!STACK 0
java.lang.ClassNotFoundException: An error occurred while automatically activating bundle com.gluonhq.eclipse.plugin (1259).
    at org.eclipse.osgi.internal.hooks.EclipseLazyStarter.postFindLocalClass(EclipseLazyStarter.java:126)
    at org.eclipse.osgi.internal.loader.classpath.ClasspathManager.findLocalClass(ClasspathManager.java:557)
    at org.eclipse.osgi.internal.loader.ModuleClassLoader.findLocalClass(ModuleClassLoader.java:331)
    at org.eclipse.osgi.internal.loader.BundleLoader.findLocalClass(BundleLoader.java:395)
    at org.eclipse.osgi.internal.loader.BundleLoader.findClassInternal(BundleLoader.java:473)
    at org.eclipse.osgi.internal.loader.BundleLoader.findClass(BundleLoader.java:422)
    at org.eclipse.osgi.internal.loader.BundleLoader.findClass(BundleLoader.java:414)
    at org.eclipse.osgi.internal.loader.ModuleClassLoader.loadClass(ModuleClassLoader.java:153)
    at java.lang.ClassLoader.loadClass(Unknown Source)
    at org.eclipse.osgi.internal.framework.EquinoxBundle.loadClass(EquinoxBundle.java:612)
    at org.eclipse.core.internal.registry.osgi.RegistryStrategyOSGI.createExecutableExtension(RegistryStrategyOSGI.java:196)
    at org.eclipse.core.internal.registry.ExtensionRegistry.createExecutableExtension(ExtensionRegistry.java:934)
    at org.eclipse.core.internal.registry.ConfigurationElement.createExecutableExtension(ConfigurationElement.java:246)
    at org.eclipse.core.internal.registry.ConfigurationElementHandle.createExecutableExtension(ConfigurationElementHandle.java:63)
    at org.eclipse.ui.internal.services.WorkbenchServiceRegistry.getSourceProviders(WorkbenchServiceRegistry.java:177)
    at org.eclipse.ui.internal.services.SourceProviderService.readRegistry(SourceProviderService.java:107)
    at org.eclipse.ui.internal.Workbench$33.runWithException(Workbench.java:2341)
    at org.eclipse.ui.internal.StartupThreading$StartupRunnable.run(StartupThreading.java:35)
    at org.eclipse.swt.widgets.Synchronizer.syncExec(Synchronizer.java:236)
    at org.eclipse.ui.internal.UISynchronizer.syncExec(UISynchronizer.java:147)
    at org.eclipse.swt.widgets.Display.syncExec(Display.java:4580)
    at org.eclipse.ui.internal.StartupThreading.runWithoutExceptions(StartupThreading.java:98)
    at org.eclipse.ui.internal.Workbench.initializeDefaultServices(Workbench.java:2336)
    at org.eclipse.ui.internal.Workbench.init(Workbench.java:1631)
    at org.eclipse.ui.internal.Workbench.runUI(Workbench.java:2804)
    at org.eclipse.ui.internal.Workbench.lambda$3(Workbench.java:623)
    at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:339)
    at org.eclipse.ui.internal.Workbench.createAndRunWorkbench(Workbench.java:563)
    at org.eclipse.ui.PlatformUI.createAndRunWorkbench(PlatformUI.java:151)
    at org.eclipse.ui.internal.ide.application.IDEApplication.start(IDEApplication.java:155)
    at org.eclipse.equinox.internal.app.EclipseAppHandle.run(EclipseAppHandle.java:203)
    at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.runApplication(EclipseAppLauncher.java:137)
    at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.start(EclipseAppLauncher.java:107)
    at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:400)
    at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:255)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at org.eclipse.equinox.launcher.Main.invokeFramework(Main.java:659)
    at org.eclipse.equinox.launcher.Main.basicRun(Main.java:595)
    at org.eclipse.equinox.launcher.Main.run(Main.java:1501)
Caused by: org.osgi.framework.BundleException: Exception in com.gluonhq.eclipse.plugin.UiPlugin.start() of bundle com.gluonhq.eclipse.plugin.
    at org.eclipse.osgi.internal.framework.BundleContextImpl.startActivator(BundleContextImpl.java:803)
    at org.eclipse.osgi.internal.framework.BundleContextImpl.start(BundleContextImpl.java:732)
    at org.eclipse.osgi.internal.framework.EquinoxBundle.startWorker0(EquinoxBundle.java:1005)
    at org.eclipse.osgi.internal.framework.EquinoxBundle$EquinoxModule.startWorker(EquinoxBundle.java:357)
    at org.eclipse.osgi.container.Module.doStart(Module.java:588)
    at org.eclipse.osgi.container.Module.start(Module.java:456)
    at org.eclipse.osgi.framework.util.SecureAction.start(SecureAction.java:471)
    at org.eclipse.osgi.internal.hooks.EclipseLazyStarter.postFindLocalClass(EclipseLazyStarter.java:117)
    ... 41 more
Caused by: java.lang.NoClassDefFoundError: org/eclipse/buildship/core/Logger
    at com.gluonhq.eclipse.plugin.UiPlugin.registerServices(UiPlugin.java:68)
    at com.gluonhq.eclipse.plugin.UiPlugin.start(UiPlugin.java:48)
    at org.eclipse.osgi.internal.framework.BundleContextImpl$3.run(BundleContextImpl.java:782)
    at org.eclipse.osgi.internal.framework.BundleContextImpl$3.run(BundleContextImpl.java:1)
    at java.security.AccessController.doPrivileged(Native Method)
    at org.eclipse.osgi.internal.framework.BundleContextImpl.startActivator(BundleContextImpl.java:775)
    ... 48 more
Caused by: java.lang.ClassNotFoundException: org.eclipse.buildship.core.Logger cannot be found by com.gluonhq.eclipse.plugin_2.6.0.v20180424-0818
    at org.eclipse.osgi.internal.loader.BundleLoader.findClassInternal(BundleLoader.java:511)
    at org.eclipse.osgi.internal.loader.BundleLoader.findClass(BundleLoader.java:422)
    at org.eclipse.osgi.internal.loader.BundleLoader.findClass(BundleLoader.java:414)
    at org.eclipse.osgi.internal.loader.ModuleClassLoader.loadClass(ModuleClassLoader.java:153)
    at java.lang.ClassLoader.loadClass(Unknown Source)
    ... 54 more

P.S: It is running now at the 2018-09 eclipse version as I updated the gluon plugin to 2.6.0v, but still not at 2018-12