I am using WordPress SEO plugin version 1.4.6 and have this issue.
XML Parsing Error: syntax error Location: http://www.pub2me.net/post-sitemap.xml Line Number 1, Column 1: 398e ^
I did not do anything, only publishing my articles. Don't install any new plugins.
I tried find similar problem, but did not find it.
If I change something in articles, setting article as draft, value 398e in first line changing.