Try to give a longer path, the most detailled possible

Assuming you want to remove the page Internal Notes (tab) from the partner form, and not a group, it would result in this without passing the name :

< xpath expr="//notebook/page[5] position="attributes">    
    < attribute name="string">Short description< /attribute>
< /xpath>

The path can be longer, and as you can see, you can tell the element's position with the []

To know which path to take, use the debug menu "Fields View Get"