There is a huge difference between an xml and a spreadsheet file. You've been asked to post a small example of your xml file. Need to see the tags that you are using. As already mentioned, the function works when you create an xml file with the LabVIEW function for that. See the earlier post if you did not do that.
If you have the file in Excel, save it as a tab separated text file. You can then use the Read from Spreadsheet File VI in the File I/O palette to read it into LabVIEW fairly simply.