Migrated data via XML doesn't import to nodes
As per this issue -- I think you need to tell MigrateSourceList where your item id's are, as an example (from isssue):

    // As with MigrateSourceMultiItems, this applies where there is not a separate
    // list of IDs to process - the source XML file is entirely self-contained.
    // For the ID path, and xpath for each component, we can use the full xpath
    // syntax as usual. However, the syntax to select the elements that correspond
    // to objects to import is more limited. It must be a fully-qualified path
    // to the element (i.e., /producers/producer rather than just //producer).
//  $item_xpath = '/producers/producer';  // relative to document
    $item_xpath = '/FMPXMLRESULT/RESULTSET/ROW';
//  $item_ID_xpath = 'sourceid';          // relative to item_xpath
    $item_ID_xpath = 'COL[1]/DATA';

    $this-&gt;source = new MigrateSourceXML($items_url, $item_xpath, $item_ID_xpath,
      $fields);


You only have 3 values in your constructor. I haven't done alot with migrating XML (just CSV and SQL). This issue is for D7 -- I think it should apply to D6.