I got this error when I was trying to create a mx DateChooser via code instead of mxml. To make a long story short the solution was to move the call to the function that was attempting it to create it. It was being called from the constructor at first and I moved it to be called after the parent object was added to the stage and that did it. If you are getting this error, try and call whatever code is causing it later in time. I hope this helps.