Here is the error log when instaling the extension into QuPath 0.5.1
Error loading extension qupath.lib.extension.monailabel.Extension@46956954: qupath/lib/gui/ActionTools
java.lang.NoClassDefFoundError: qupath/lib/gui/ActionTools
at qupath.lib.extension.monailabel.Extension.installExtension(Extension.java:44)
at qupath.lib.gui.ExtensionManager.refreshExtensions(ExtensionManager.java:148)
at qupath.lib.gui.ExtensionManager.promptToCopyFilesToExtensionsDirectory(ExtensionManager.java:261)
at qupath.lib.gui.viewer.DragDropImportListener.handleFileDropImpl(DragDropImportListener.java:334)
at qupath.lib.gui.viewer.DragDropImportListener.handleFileDrop(DragDropImportListener.java:286)
at qupath.lib.gui.viewer.DragDropImportListener.lambda$handle$0(DragDropImportListener.java:196)
at com.sun.javafx.application.PlatformImpl.lambda$runLater$10(PlatformImpl.java:456)
at java.base/java.security.AccessController.doPrivileged(Unknown Source)
at com.sun.javafx.application.PlatformImpl.lambda$runLater$11(PlatformImpl.java:455)
at com.sun.glass.ui.InvokeLaterDispatcher$Future.run(InvokeLaterDispatcher.java:95)
at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
at com.sun.glass.ui.win.WinApplication.lambda$runLoop$3(WinApplication.java:185)
at java.base/java.lang.Thread.run(Unknown Source)
Caused by: java.lang.ClassNotFoundException: qupath.lib.gui.ActionTools
at java.base/java.net.URLClassLoader.findClass(Unknown Source)
at java.base/java.lang.ClassLoader.loadClass(Unknown Source)
at java.base/java.lang.ClassLoader.loadClass(Unknown Source)
... 13 more
Here is the error log when instaling the extension into QuPath 0.5.1