Scenario:
Create JavaFX Sample Project using the "FXML Login Demo" project.

build & run --> OK

Edit the login.fxml file using SceneBuilder and move controls around on the canvas, save the modified file.

build & run --> fails (stack trace below)

attempt to edit same bug in SceneBuilder again --> fails (see screenshots)

error3.jpg: the login.fxml as it appears when first opened in SceneBuilder (all nodes appear in Hierarchy)
error2.jpg:the edited login.fxml before saving and exiting SceneBuilder. Note that it is missing nodes in the Hierarchy view
error.jpg: error when attempting to edit fxml after previously having edited it

===
Unable to coerce [TextField[id=userId, styleClass=text-input text-field], PasswordField[id=password, styleClass=text-input text-field password-field], Label[id=x1, styleClass=label], Label[id=x2, styleClass=label], Label[id=errorMessage, styleClass=label], Button[id=login, styleClass=button]] to class javafx.scene.Node.
/C:/Documents%20and%20Settings/jbmcglyn.ST-USERS/My%20Documents/NetBeansProjects/FXML-LoginDemo3/build/classes/demo/login.fxml:46
  at com.sun.javafx.fxml.BeanAdapter.coerce(BeanAdapter.java:720)
  at javafx.fxml.FXMLLoader$Element.add(FXMLLoader.java:126)
  at javafx.fxml.FXMLLoader$ValueElement.processEndElement(FXMLLoader.java:609)
  at javafx.fxml.FXMLLoader.processEndElement(FXMLLoader.java:2421)
  at javafx.fxml.FXMLLoader.load(FXMLLoader.java:2129)
  at javafx.fxml.FXMLLoader.load(FXMLLoader.java:2021)
  at javafx.fxml.FXMLLoader.load(FXMLLoader.java:2733)
  at javafx.fxml.FXMLLoader.load(FXMLLoader.java:2712)
  at javafx.fxml.FXMLLoader.load(FXMLLoader.java:2698)
  at demo.App.replaceSceneContent(App.java:115)
  at demo.App.gotoLogin(App.java:108)
  at demo.App.start(App.java:72)
  at com.sun.javafx.application.LauncherImpl$5.run(LauncherImpl.java:319)
  at com.sun.javafx.application.PlatformImpl$5.run(PlatformImpl.java:206)
  at com.sun.javafx.application.PlatformImpl$4.run(PlatformImpl.java:173)
  at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
  at com.sun.glass.ui.win.WinApplication.access$100(WinApplication.java:29)
  at com.sun.glass.ui.win.WinApplication$2$1.run(WinApplication.java:62)
  at java.lang.Thread.run(Thread.java:722)

Jun 22, 2012 11:59:49 AM demo.App gotoLogin
SEVERE: null
java.lang.IllegalArgumentException: Unable to coerce [TextField[id=userId, styleClass=text-input text-field], PasswordField[id=password, styleClass=text-input text-field password-field], Label[id=x1, styleClass=label], Label[id=x2, styleClass=label], Label[id=errorMessage, styleClass=label], Button[id=login, styleClass=button]] to class javafx.scene.Node.
at com.sun.javafx.fxml.BeanAdapter.coerce(BeanAdapter.java:720)
at javafx.fxml.FXMLLoader$Element.add(FXMLLoader.java:126)
at javafx.fxml.FXMLLoader$ValueElement.processEndElement(FXMLLoader.java:609)
at javafx.fxml.FXMLLoader.processEndElement(FXMLLoader.java:2421)
at javafx.fxml.FXMLLoader.load(FXMLLoader.java:2129)
at javafx.fxml.FXMLLoader.load(FXMLLoader.java:2021)
at javafx.fxml.FXMLLoader.load(FXMLLoader.java:2733)
at javafx.fxml.FXMLLoader.load(FXMLLoader.java:2712)
at javafx.fxml.FXMLLoader.load(FXMLLoader.java:2698)
at demo.App.replaceSceneContent(App.java:115)
at demo.App.gotoLogin(App.java:108)
at demo.App.start(App.java:72)
at com.sun.javafx.application.LauncherImpl$5.run(LauncherImpl.java:319)
at com.sun.javafx.application.PlatformImpl$5.run(PlatformImpl.java:206)
at com.sun.javafx.application.PlatformImpl$4.run(PlatformImpl.java:173)
at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
at com.sun.glass.ui.win.WinApplication.access$100(WinApplication.java:29)
at com.sun.glass.ui.win.WinApplication$2$1.run(WinApplication.java:62)
at java.lang.Thread.run(Thread.java:722)