Scenario:
"I have some blog items which use extended characters, such as "ñ" which is obtained by holding the "alt" key and entering "0241" on the numeric keypad. The character displays fine in the item on the blog, but the RSS feed stops with the following error when it reaches the items in question:
"An invalid character was found in text content.
Solution:
Make sure Nucleus is outputting your RSS feed with the correct coding by checking the following line of code is the first line in the Main Index part of your "feeds/rss20" skin:
<?xml version="1.0" encoding="<%charset%>"?>
Original forum thread (thanks, ftruscot!):
http://forum.nucleuscms.org/viewtopic.php?t=14870