Xinclude trouble

Hi,

I am trying to use the XInclude feature, but I don't manage to make it 
happen...

my call is from com/soft/iseult/iseult/gui/MainMenu.xml, rendered by the 
class com/soft/iseult/iseult/gui/MainMenu
<menubar>
...
     <menu id="inputMenu" text="menu.input" mnemonic="VK_E" 
include="ListsMenuFragments.xml#INPUT_IO_ACTIONS"/>
...
</menubar>

and ListsMenuFragments.xml (in the same com/soft/iseult/iseult/gui 
package) looks like :
<?xml version="1.0" encoding="UTF-8" ?>
<list>
     <menu id="INPUT_EDIT_ACTIONS">
         <menuitem action="processCopyAction"/>
         <menuitem action="processMoveAction"/>
     </menu>
     <menu id="INPUT_IO_ACTIONS">
         <menuitem action="addDirAction"/>
         <menuitem action="addImgAction" accelerator="control O"/>
     </menu>
</list>
<list type="OUTPUT">
     <menu id="OUTPUT_EDIT_ACTIONS">
         <menuitem action="transferCopyAction"/>
         <menuitem action="transferMoveAction"/>
     </menu>
     <menu id="OUTPUT_IO_ACTIONS">
         <menuitem action="outputDirAction" accelerator="control S"/>
     </menu>
</list>
</list>

But whatever I change the include call to (I tried to prefix it with the 
name of the package), I get that error :
org.jdom.input.JDOMParseException: Error on line 1: 
java.lang.NullPointerException
java.lang.Exception: Invalid SwiXML Descriptor.
	at org.swixml.SwingEngine.render(Unknown Source)

Has anyone had better success with XInclude?? Because with the only 
sample released, I don't see where I'm wrong

Thx,
Tristan