BP 1.2.3: Sitewide Activity RSS Feed


We have Buddypress 1.2.3 installed on WPMU 2.9.2, and the RSS feed for our Sitewide Activity is not working properly. We receive the following error message:

XML Parsing Error: XML or text declaration not at start of entity
Location: http://www.generation-europe.eu/summit2010/activity/feed/
Line Number 2, Column 1:<?xml version="1.0" encoding="UTF-8"?>

After searching different WP support forums, I found a potential solution: adding the following lines of code to the PHP file that generates the RSS feed:
$out = ob_get_contents();
$out = str_replace(array("\n", "\r", "\t", " "), "", $input);

I added these lines to the file /buddypress/bp-activity/feeds/bp-activity-sitewide-feed.php, but that seems to break the RSS feed entirely (blank page, not even an error message). I did notice the BuddyPress PHP feed files do not have the "$more = 1;" line as do the regular WordPress PHP feed files. Don't know if that's part of the problem...

Any ideas what I should try next?