Invalid characters in xml
Sounds like the file you downloaded is actually not an XML file yet. It is actually a compressed XML file, and was probably compressed using the GZip algorithm.

To see your data you will have to decompress it:


rename the file to an .xml.gz extension (if it doesn't have one already)
use any decompression program to decompress your XML data (7zip is good/free)
open the resulting XML file in your favourite text editor!