WordPress version: 3.5.1
WordPress SEO version: 1.4.3
The plugin generated 287 characters of unexpected output during activation. If you notice “headers already sent” messages, problems with syndication feeds or other issues, try deactivating or removing this plugin.
I performed a downgrade to version 1.4.2 and the same problem persists. The 1.3.4.4 version installs without this error, but the error with the XML sitemap happen again.