the parsing error you are reporting is caused by three blank lines that precede the XML declaration of your Google Sitemap and I'm almost sure they are not related to a bug.
There could be a script/plugin in your instal that outputs the blank lines before SiteTree sends the XML document to the browser/client or a "hidden" (visible only in the error log file) PHP error that generates them.
The only way to fix it, it's to find the cause. First, try the following:
• Click on the "Rebuild" button, visit the Sitemap, refresh the webpage and finally check the error log file of your server.
If you find something related to SiteTree, you may post it here. Otherwise go on:
• Open the
wp-config.php file and temporarily replace the line
define( 'WP_DEBUG', false );
define( 'WP_DEBUG', true );
ini_set( 'error_reporting', E_ALL );
Now, repeat the steps listed in the first point but this time, take a look at the source code of the Google Sitemap too.
If you still haven't found any error, the problem isn't due to a bug nor to a PHP error. To check if the trouble comes from another plugin, you could attempt this:
• Open the file
/wp-content/plugins/sitetree/core/sitetree.class.php. In line 20 you should read
const DEBUG_MODE = false;
Now, deactivate, one by one, all of your plugins and each time reload the Google Sitemap in your browser window by checking if the parsing error goes away.
In case you don't find the cause, you could ask a developer to debug your theme and/or your WordPress installation.