when I click on the link for the posts http://www.telechargercours.com/post-sitemap.xml I receive an error

XML Parsing Error: not well-formed
Location: http://www.telechargercours.com/post-sitemap.xml
Line Number 14427, Column 34: <image:caption>L'Ordre SELECT Élémentaire</image:caption>

any idea about this error?

I suspect that the character you used for either the É or é is not in the UTF-8 character set.