[new blog template] error on save blog as template

well got this on saving the blog as a template... AND stting it as default

Warning: Cannot modify header information - headers already sent by (output started at /home/mgr/public_html/wp-content/mu-plugins/blogtemplatesfiles/blog_templates.php:521) in /home/mgr/public_html/wp-includes/functions.php on line 830

Warning: Cannot modify header information - headers already sent by (output started at /home/mgr/public_html/wp-content/mu-plugins/blogtemplatesfiles/blog_templates.php:521) in /home/mgr/public_html/wp-includes/functions.php on line 831

huh ?