The following FXML code will cause SceneBuilder 1.1 to fail with a null exception:

<ComboBox fx:id="dbCombo"><items></items></ComboBox>

Screen shot attached. The code compiles fine under Netbeans. Removing the <items></items> the error no longer occurs.

If you double click on the FXML from within Netbeans, you get the error shown in the screen shot, and a SceneBuilder process still exists (it doesn't die gracefully after the error, nor does itever open.)

Also, even after killing the stray SceneBuilder process, you can no longer open ANY FXML file from Netbeans in SceneBuilder - Netbeans goes off into lala land.