Header(Location url) not passing parameters

I have a form in the file index.php that sends its post log-in parameters to the script 'login.php'.

If the password is wrong i call the following function: header("Location: absPath/index.php?error=1") from the login.php file. Although the functions sends me to the right page, the parameter is not sent. If i do a var_dump($_GET), it will print an empty array.

Any ideas?