WordPress RSS feed error – instruction target matching is not allowed

WordPress RSS feed error

WordPress RSS feed error

Yesterday I met this error when tried to burn my WordPress blog feed at the feedburner.google.com:
“The URL does not appear to reference a valid XML file. We encountered the following problem: Error on line 6: The processing instruction target matching “[xX][mM][IL]” is not allowed”.

After checking feed page source code I discovered that it really has 6 blank rows before the first valid XML tag. So the problem is found but what is the source of such blank lines at the very beginning of the feed page? Thanks to the curious guys, after 30 minutes of Google reseaching I found these very useful for me posts:

1st) http://www.techbuzz.in/error-on-line-2-the-processing-instruction-target-matching-xxmmll-is-not-allowed.php
2nd) http://www.flyaga.info/en/wordpress/plugins/fix-rss-feed-error-wordpress-plugins.htm
I catched the idea and looked at my files. A few blank lines were found after closing ?> PHP tag at some plugins and the function.php file from blog theme. After removing them the problem was gone.

Finally, if you are PHP developer, you need be aware of possible problem having empty blank lines after ?> closing PHP tag. So the better to not have them at your code.