jQuery Grid Plugin - jqGrid

Hi all -

I'm new to jqGrid, and I'm trying to work through the example grid. When I run it, I get the caption, header, body, and navigation layers, but the body is empty. The "Loading ..." message flashes briefly, but nothing shows up, and I don't get any error messages.

My Javascript code is:

          jQuery("#list").jqGrid({
            url:MyURL,
            datatype: 'xml',
            mtype: 'GET',
            colNames:['Inv No','Amount','Tax','Notes'],
            colModel :[
              {name:'invid', index:'invid', width:55},
              {name:'amount', index:'amount', width:80, align:'right'},
              {name:'tax', index:'tax', width:80, align:'right'},
              {name:'note', index:'note', width:150, sortable:false}
            ],
            pager: '#pager',
            rowNum:10,
            rowList:[10,20,30],
            sortname: 'invid',
            sortorder: 'desc',
            viewrecords: true,
            caption: 'My first grid'
          });

and the XML that is returned is (this is when I just to a GET to the server and display the result:

 <?xml version='1.0' encoding='utf-8'?>
 <rows>
 <page>1</page>
 <total>1</total>
 <records>2</records>
 <row id='1'>
 <cell>101</cell>
 <cell>500.00</cell>
 <cell>15.00</cell>
 <cell>Testing</cell>
 </row>
 <row id='2'>
 <cell>102</cell>
 <cell>200.00</cell>
 <cell>10.00</cell>
 <cell>Testing2</cell>
 </row>
 </rows>

I assume I'm missing something obvious, but I've been working with it all afternoon and I just don't see it. Can anyone point me in the right direction?

Thanks very much,