cannot login after uploading site.

i created a theme and database… some pages of websites looks fine after being uploaded in the server. but cannot login to edit instead shows following error message. what should i do?

Warning: Cannot modify header information – headers already sent by (output started at /home/rtibet/public_html/wp-content/themes/avionline/functions.php:69) in /home/aonline/public_html/wp-login.php on line 444