The processing instruction target matching “[xX][mM][lL]” is not allowed

I recently encountered this error two days ago when I try to change my feedburner feeds to enable podcasting feeds. After adding additional wordpress plugins there it goes my feeds suddenly doesn’t seem to work. Code error creeps in our site and it has been a headache for a while. So the trouble shooting begins: First I try to resolve the error from my RSS feeds by going to www.feedvalidator.org the site give me the following solution so I followed the steps faithfully.

Solution
* PHP also uses a similar notation: . Note that the final php ?> should be omitted from all PHP code files—modules, includes, etc. The closing delimiter is optional in PHP (but not in XML), and removing it helps prevent unwanted white space at the end of files which can cause problems with your feeds.
* Check your wp-rss2.php and wp-atom.php files for blank lines outside of bracketed sections.
* Check your wp-config.php file for blank lines outside of bracketed sections.
* Check your theme’s functions.php file for blank lines outside of bracketed sections.
* One by one, disable plugins and revalidate until you isolate the one causing the problem.

So the final solution is to disable the plugins we’re using which is quite painful especially if you’re site’s layout are dependent on the plugins that you are using. So you’re solution would be either to ignore your RSS; error or do it painfully and start troubleshooting. Of course the reward would be excellent. See now my feeds are working.