Don't know why I didn't see this before.... <img>
RSS is very sensitive by nature, the most common reason for getting an invalid character error when validating the feed is because of text editors. If you use a text editor, mainly one based in Windows(Word, wordpad, etc.) they use different special characters.
For example, this is single apostrophe typed here in the text box '
Here is a single apostrophe copied from Microsoft Word à¢Ãƒ ¢Ã¢â‚¬Å¡Ã‚ ¬Ãƒâ€¹Ã…“
You can see the difference, the second one, from Word is an invalid character and will return errors.
The best thing to do is try and hunt down the invalid characters using a feed validator.
I recommend
http://feedvalidator.org as I've had success with it.
Use the URL
http://www.mysite.com/subforum/news_rss.phpSo, your URL would be
http://www.balloontrader.com/lta/news_rss.phpIt looks like it is the Windows issue, fix that one post with the invalid single quote and see if that gets your feed working again. Most other validation errors can be ignored if your feed is working.