Mysqli log-in results in a blank page when placed online.

I am using the new Mysqli SB tool (which is really great BTW) to create a user log-in and update system. I have followed the tutorial and on my local computer, everything works as expected. The user can log-in and update their information, etc. However, the same files installed on the live server result in a blank page when one tries to log-in.Obviously, I have overlooked something really simple but I cannot get to the bottom of the problem. FYI - much of the site has been updated to work with Mysqli so this question is specific to the Log-in function. Many thanks for any advice.

a blank page means that a php error is occurring but error reporting is turned off.

to turn error reporting on, add the following code at line 1:

<?php
error_reporting(E_ALL);
ini_set('display_errors','on');
?>

once we know what the error is, we will be able to troubleshoot the cause.

Thanks - here is the result:

Warning: Cannot modify header information - headers already sent by (output started at /home/httpd/vhosts/website.ch/httpdocs/portfolio/log-in.php:6) in /home/httpd/vhosts/website.ch/httpdocs/webassist/mysqli/authentication.php on line 138

("website.ch" has been substituted for the actual server address)

this means there is output such as a blank line between a closing php tag:
?>

and an opening php tag:
<?php

around line 6 of the log-in.php page.


see this thread for details on troubleshooting the headers already error:
http://www.webassist.com/forums/posts.php?id=19285

Many thanks - it worked. As I said in my original post, I obviously overlooked something basically simple.
Your support is really great!

you're welcome.