logging in/out leads to blank page

Hi all.

I'm having a bit of an issue with the theme that I am creating. This is my first Drupal theme, so you could say I am a bit of a newbie.

When I log in and log out (as well as various other times navigating in Admin), the site refreshes to a "blank" page. When I hit refresh it brings up the correct page. When this is after a logout, the refreshed page has an "access denied" message. This happens on a local Xampp installation as well as my test server installation.

I know that this is an issue with my theme because I have tried it using Garland and the problem goes away.

Where do I need to start looking for the problem? What am I looking for? I have error reporting to the screen turned on but haven't seen anything.

Here is what I have found in my error logs that might be helpful:
Location http://localhost/drupal/?q=frontpage&destination=frontpage
Referrer http://localhost/drupal/
Message Cannot modify header information - headers already sent by (output started at C:\xampp\htdocs\drupal\themes\aaswg-rose\template.php:9) in C:\xampp\htdocs\drupal\includes\common.inc on line 309.

and

Location http://localhost/drupal/?q=frontpage&destination=frontpage
Referrer http://localhost/drupal/
Message session_regenerate_id() [function.session-regenerate-id]: Cannot regenerate session id - headers already sent in C:\xampp\htdocs\drupal\includes\session.inc on line 103.

I am using Drupal 5.2.
Any thoughts?

Thanks,

Shrill