[PHP] Headers already sent (Sometimes)

Im getting Warnings about headers being already sent. But not on my local web server Im sending the headers (to try and make the page not cache) before anything is echoed to the browser. I set the error reporting to E_ALL at the top of the script, turning error reporting off suppresses the warnin

[PHP] Authentication session problem (php/server implementation?)

I have a user authentication system using sessions it checks username and password against a database. if correct it sets a variable in the session cookie (via $_SESSION) and redirects to the protected page which checks for that variable. if the user/pass is wrong it redirects to an error page. if