Problem with 2.7.1

Hey,
I had a site that was working fine with the older version, and ive tried everything to fix it, basically i upgraded to 2.7.1 and then it wouldnt let me log in. whenever i try i get this:

Warning: Cannot modify header information – headers already sent by (output started at /home/phoenix/public_html/karoken.com/wp-includes/functions.php:2945) in /home/phoenix/public_html/karoken.com/wp-login.php on line 255

Warning: Cannot modify header information – headers already sent by (output started at /home/phoenix/public_html/karoken.com/wp-includes/functions.php:2945) in /home/phoenix/public_html/karoken.com/wp-login.php on line 267

Warning: Cannot modify header information – headers already sent by (output started at /home/phoenix/public_html/karoken.com/wp-includes/functions.php:2945) in /home/phoenix/public_html/karoken.com/wp-includes/pluggable.php on line 649

Warning: Cannot modify header information – headers already sent by (output started at /home/phoenix/public_html/karoken.com/wp-includes/functions.php:2945) in /home/phoenix/public_html/karoken.com/wp-includes/pluggable.php on line 650

Warning: Cannot modify header information – headers already sent by (output started at /home/phoenix/public_html/karoken.com/wp-includes/functions.php:2945) in /home/phoenix/public_html/karoken.com/wp-includes/pluggable.php on line 651

Warning: Cannot modify header information – headers already sent by (output started at /home/phoenix/public_html/karoken.com/wp-includes/functions.php:2945) in /home/phoenix/public_html/karoken.com/wp-includes/pluggable.php on line 850

i reinstalled wordpress just now, from scratch, so nothing has been edited, its just wordpress on my site.. i have no idea what the problem is.