I am having the same problem. Running a new install of 2.5.1 and copied NextGen .97 build to the plugins folder. uploaded the image rotators then when I click activate I receive the following similar errors:
Warning: Cannot modify header information – headers already sent by (output started at /home/guuroo/public_html/piper/wp-content/themes/beautiful-sunrise-10/functions.php:72) in /home/guuroo/public_html/piper/wp-includes/pluggable.php on line 694
Any recommendations on how to fix this? This is my second clean install of WP and NextGen and all I get are errors when I activate.