Error using Utopia Plugin

I just set up my blog a couple of weeks ago and am trying to use David Pankhurst’s Utopia plugin. I followed the instructions to the letter, and when I activate it, I get this error message when I go into …/blog/wp-admin/

Warning: Cannot modify header information – headers already sent by (output started at /home/dogsup/public_html/blog/wp-content/plugins/utopia1.php:104) in /home/dogsup/public_html/blog/wp-admin/admin.php on line 10

for lines 10, 11, 12, 13, which are all the header lines in admin.php. This error comes up for other files that have the same header-type lines in them, throwing the same error with the accessed filename and line numbers.

I’ve changed access permissions to everything I thought might be affected. Any suggestions? I’m totally stumped.