RSS problems

I installed the Feedburner module, got that set up and then went to Feedburner to burn our feed. I got this:

XML Parsing error: syntax error
Explanation

Your feed is not well formed according to the XML specification. All feeds must be well-formed XML. In fact, IE7 and the RSS platform in Windows Vista only support feeds that are well-formed XML.
Solution

The text of the error may contain additional helpful details. At a minimum, the actual line and column number where the error was detected will be reported.

The most common cause is encoding errors. There are several basic approaches to solving this: escaping problematic characters ("<" becomes "<", "&" becomes "&", etc.), escaping entire blocks of text with CDATA sections, or putting an encoding declaration at the start of the feed.

Another common error is the inclusion of whitespace characters (spaces, tabs, newlines) before the XML Declaration. If an XML Declaration is included, it must be the first thing in the document
Not clear? Disagree?

You might be able to find help in one of these fine resources.

But how do I fix the file? I can't find a rss.xml file on our server to even look to see if i can find the error.