shorty's dashboard

Upgraded WordPress to 2.6, downloaden v1.2 of ChaoticSoul theme (i was using 1.0), after activation of the new theme the following error appeared: "Warning: call_user_func_array() [function.call-user-func-array]: First argument is expected to be a valid callback, 'header_style' was given in /var/www/html/wp-includes/plugin.php on line 311". All plugins disabled accept akismet! v1.0 hasn't got this problem. Any ideas?