I have an unwanted empty line at the beginning of the document and I can't find the reason why it is happening. For default HTML I wouldn't have minded it but RSS doesn't work. I disabled all the plugins and no luck; the plugins don't cause anything. I started having this issue after I changed the file owner and permissions a long time ago but didn't care at the time. My permissions for all files and folders in the theme are "rwxr-xr-- myusername:www-data". I tried to add comments at the beginning of header.php, had no luck. The line exists even in /wp-admin. wp-login.php doesn't have it though. Where should I look for this line?