Solved it:
I just solved the problem. In my case I could not have any permision set to 777 and I had to change them to 755. Because of the security issues files with permission set to 777 are automatically blocked by my server provider.
Can’t login to WP admin page on my site. I am getting the same error:
The server encountered an unexpected condition which prevented it from fulfilling the request.
Installed ‘XML Sitemap Generator for WordPress 3.1.6’ could not generate Sitemap.xml. Changed ‘root’ permission to 777. Ran generator again and that’s when I got this error.
Any ideas how to recover from this?