Multiple Plugin Install for WPMU & BuddyPress

I have installed multiple plugins within the mu-plugins directory of my site... I have installed all files according to the install.txt files. I recieve this error on all plugins....

Warning: Cannot modify header information - headers already sent by (output started at /home/mccomm/public_html/wp-admin/admin-header.php:18) in /home/mccomm/public_html/wp-includes/pluggable.php on line 868

Any help or suggestions would be appreciated, thanks..