Re: Header already sent / XML cannot be displayed When user logs in
Looks like it is a little "bug"
Actually , you are using a rss id which does not exist asCheck the rss you use actually exist.
Anyway, tw should verify it's an existing feed, the correction in lib/tikilib.php before line before 5524 would be to add:

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$items = $rsslib->parse_rss_data($rssdata, $id); // add that line if (!$items) continue; $repl="";
I hope that will help