After upgrading to 2.5.7 (WP version 3.2.1) I get the following error:
Warning: Cannot modify header information - headers already sent by (output started at /XXX/wp-content/plugins/wp-htaccess-control/wp-htaccess-control.php:1) in /XXX.pl/wp-content/plugins/wp-super-cache/wp-cache-phase2.php on line 77
I did upgrade one more site on the same hosting machine and it works fine (the config for wp-htaccess-control and wp-supercache is EXACTLY the same on both sites). I tried refreshing the cache for wp-supercache and resaving the options in your plugin. Didn't work. It did work fine prior the latest update.
Please look into this.