WordPress MU

My install seems ok at http://www.mba365.com and I was able to add new blogs and they show up fine (eg cornell.mba365.com)...but i'm getting weird messages.

#1: When i login to the backend of my site, this appears up top:
Warning: Cannot modify header information - headers already sent by (output started at /home/content/s/t/a/startuplabnet/html/wp-admin/includes/mu.php:1) in /home/content/s/t/a/startuplabnet/html/wp-includes/functions.php on line 798

Warning: Cannot modify header information - headers already sent by (output started at /home/content/s/t/a/startuplabnet/html/wp-admin/includes/mu.php:1) in /home/content/s/t/a/startuplabnet/html/wp-includes/functions.php on line 799

#2. When i go to edit a post, i get the following:
Warning: Cannot modify header information - headers already sent by (output started at /home/content/s/t/a/startuplabnet/html/wp-admin/includes/mu.php:1) in /home/content/s/t/a/startuplabnet/html/wp-includes/pluggable.php on line 868

It appears even though I'm getting the error message, that whatever i try to do after an update is working correctly. So i'm stumped as to what these messages might be.

Can anyone offer some words of wisdom??

They're not error messages - just warnings.

Check for a trailing blank line after the closing ?> in your config.php file.

Also you should really change your PHP settings so that warnings don't go the the screen but go to an error log.

thanks steve..i know this is prob a stupid question..but where the config.php file? And where exactly do i change settings for the error log?