I installed this plugin (http://boakes.org/analytics) in my MU WordPress, I actived it without problems but when the users try to add their own code they get this error:
Warning: Cannot modify header information - headers already sent by (output started at /XX/blogs/wp-admin/admin-header.php:16) in /XX/blogs/wp-includes/functions.php on line 1133
Do you know how can I fix it?