<Ui2DAnimation item="A_HotButton1Normal">
<Ui2DAnimation item="A_HotButton1Pressed">
<Ui2DAnimation item="A_HotButton1PressedFlyby">
<Ui2DAnimation item="A_HotButton1Disabled">
<Pieces>HB4_FileButton</Pieces>
Each Hotbutton (1 - 10) Should have the above Ui2Animation item.
You should have a <Pieces> file listed above also.
I have never seen an XML reference error! Ui2DAnimation[6]:HB_OptionsFlyby[583]
(583) is the line of code to check.
Hope that helps a little...