Fatal error: main() [function.require]: Failed opening required './wp-blog-header.php' (include_path='.:/usr/lib/php') on line 17

Fatal error: main() [function.require]: Failed opening required './wp-blog-header.php' (include_path='.:/usr/lib/php')  on line 17

Not sure what happened, either there was an error while I was updating the blog's header, and wp-blog-header.php was deleted, or something 1and1 was having an issue.

Anyway, the solution is to restore wp-blog-header.php to the root folder of your blog, which can be found in your original wordpress installation zip file.

For example, if I had a blog at imadethisdesign.com/blog, and I received this error, then I would download a copy of WordPress, then unzip it, then copy the wp-blog-header.php to imadethisdesign.com/blog

Also, you can try this solution as well when the above does not work:
http://wordpress.org/support/topic/wp-blog-headerphp-failed-to-open-stream

All should be well.