Sitemap.xml errors

I'm getting the following errors when trying to view

Warning: file_put_contents(//home/sportsfg/public_html/wp-content/blogs.dir/1/files/sitemap.xml) [function.file-put-contents]: failed to open stream: Permission denied in /home/sportsfg/public_html/wp-content/mu-plugins/simple-sitemaps.php on line 177

Warning: Cannot modify header information - headers already sent by (output started at /home/sportsfg/public_html/wp-content/mu-plugins/simple-sitemaps.php:177) in /home/sportsfg/public_html/wp-content/sitemap.php on line 29

I tried changing blogs.dir to 777 and access it again but same error msgs. One thing I noticed is that file-put-contents is:

file_put_contents( "$filename/$file", $content );

and my blogs.dir paths are /1/files (plural). Could that be an issue? I vaguely remember changing it to files some time ago due to image and avatar upload issues.