WordPress RSS Feed XML Error
In WordPress if the following error appears on selecting the RSS feed
XML Parsing Error: XML declaration not at start of external entity
Then check for a new Plugin’s installed having spaced in between the lines. You can check this using the Plugin Editor. After removing the extra spaces between the lines this error should get resolved.
Displaying of Duplicate Post
After upgrading to WordPress 2.5 from WordPress 2.02 encountered a problem with the display of posts in the blog as well as RSS feeds. Some of the posts were displaying more than once. The reason for this is because of the Category Visibility-RH Rev. After de-activating the Plugin the problem got resolved.