Same host, same problem.
Your gallery.xml file also starts with <!--xml version="1.0" encoding="UTF-8"?>
It should be <?xml version="1.0" encoding="UTF-8"?>
After a little investigation, I can confirm that the file is being changed by the host (webs.com) when it is uploaded via their control panel (FTP is not available on their free accounts but probably wouldn't make any difference).
I tried changing the file extension to .txt but as soon as I uploaded, <? reverted to <!--. I then tried editing the file via their control panel but as soon as I saved it, <? reverted to <!-- once again.
However, coinslab seems to have managed to change it and have it stick.
Perhaps coinslab can let us in on the secret!
In the meantime, my advice? Change host.
SimpleViewer Support Team.