I recently got the nasty “XML Parsing Error: XML or text declaration not at start of entity Location” error instead of RSS feed on two client WordPress sites. First, I tried the Fx-RSS-Feed plugin. No luck! it identified several hundred WordPress and theme files with unnecessary whitespace. Most of the files were write-protected. Way too much work for me to change all the permissions, run the plugin, and change them back. Instead, I used the fix at Wejn’s lair. Scroll down the page and download the file “wejnswpwhitespacefix.php” or get the text version here.