Try to open attached file.
I've got following exception.
Note that it's document from manual tests and this issue is regression.

java.io.IOException: javafx.fxml.LoadException:
/D:/work/authoring/authoringtool_test/ManualSuite/data/css/CustomFXML.fxml:19

at com.oracle.javafx.scenebuilder.kit.fxom.FXOMLoader.load(FXOMLoader.java:92)
at com.oracle.javafx.scenebuilder.kit.fxom.FXOMDocument.<init>(FXOMDocument.java:75)
at com.oracle.javafx.scenebuilder.kit.editor.EditorController.updateFxomDocument(EditorController.java:1796)
at com.oracle.javafx.scenebuilder.kit.editor.EditorController.setFxmlTextAndLocation(EditorController.java:563)
at com.oracle.javafx.scenebuilder.app.DocumentWindowController.loadFromFile(DocumentWindowController.java:347)
at com.oracle.javafx.scenebuilder.app.SceneBuilderApp.performOpenFiles(SceneBuilderApp.java:432)
at com.oracle.javafx.scenebuilder.app.SceneBuilderApp.performOpenFile(SceneBuilderApp.java:381)
at com.oracle.javafx.scenebuilder.app.SceneBuilderApp.performControlAction(SceneBuilderApp.java:135)
at com.oracle.javafx.scenebuilder.app.menubar.MenuBarController$ApplicationControlActionController.perform(MenuBarController.java:1497)
at com.oracle.javafx.scenebuilder.app.menubar.MenuBarController.handleOnActionMenu(MenuBarController.java:1041)
at com.oracle.javafx.scenebuilder.app.menubar.MenuBarController.access$900(MenuBarController.java:88)
at com.oracle.javafx.scenebuilder.app.menubar.MenuBarController$19.handle(MenuBarController.java:1034)
at com.oracle.javafx.scenebuilder.app.menubar.MenuBarController$19.handle(MenuBarController.java:1030)
at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:86)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:49)
at javafx.event.Event.fireEvent(Event.java:204)
at javafx.scene.control.MenuItem.fire(MenuItem.java:462)
at com.sun.javafx.scene.control.skin.ContextMenuContent$MenuItemContainer.doSelect(ContextMenuContent.java:1344)
at com.sun.javafx.scene.control.skin.ContextMenuContent$MenuItemContainer.doSelect(ContextMenuContent.java:1319)
at com.sun.javafx.scene.control.skin.ContextMenuContent$MenuItemContainer$7.handle(ContextMenuContent.java:1287)
at com.sun.javafx.scene.control.skin.ContextMenuContent$MenuItemContainer$7.handle(ContextMenuContent.java:1285)
at com.sun.javafx.event.CompositeEventHandler$NormalEventHandlerRecord.handleBubblingEvent(CompositeEventHandler.java:218)
at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:80)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:54)
at javafx.event.Event.fireEvent(Event.java:204)
at javafx.scene.Scene$MouseHandler.process(Scene.java:3689)
at javafx.scene.Scene$MouseHandler.access$1800(Scene.java:3414)
at javafx.scene.Scene.impl_processMouseEvent(Scene.java:1676)
at javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:2467)
at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:314)
at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:243)
at java.security.AccessController.doPrivileged(Native Method)
at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:345)
at com.sun.glass.ui.View.handleMouseEvent(View.java:526)
at com.sun.glass.ui.View.notifyMouse(View.java:898)
at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
at com.sun.glass.ui.win.WinApplication.access$300(WinApplication.java:39)
at com.sun.glass.ui.win.WinApplication$4$1.run(WinApplication.java:112)
at java.lang.Thread.run(Thread.java:744)
Caused by: javafx.fxml.LoadException:
/D:/work/authoring/authoringtool_test/ManualSuite/data/css/CustomFXML.fxml:19

at javafx.fxml.FXMLLoader.constructLoadException(FXMLLoader.java:2611)
at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2589)
at javafx.fxml.FXMLLoader.load(FXMLLoader.java:2419)
at com.oracle.javafx.scenebuilder.kit.fxom.FXOMLoader.load(FXOMLoader.java:89)
... 55 more
Caused by: java.lang.IllegalStateException
at com.oracle.javafx.scenebuilder.kit.fxom.TransientObject.makeFxomObject(TransientObject.java:157)
at com.oracle.javafx.scenebuilder.kit.fxom.FXOMLoader.endElement(FXOMLoader.java:269)
at javafx.fxml.FXMLLoader.processEndElement(FXMLLoader.java:2836)
at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2526)
... 57 more