I have been setting up all of the options for the supporter features using the supporter plugin.
Everything was going fine, until I logged in as a test user and found that if I clicked either of the "premium Themes" links I get an Internal Server Error.
I checked the server error log and the most recent one is this:
[Wed Dec 30 11:48:48 2009] [error] [client 188.8.131.52] Premature end of script headers: themes.php, referer: http://URL/wp-admin/plugins.php
Now even if I am logged in with the admin account I get the error.