no space, no carriage return. A common
case is having extra blank at the end of an included script file.<br>
If you can't figure out where the problem comes from, this other message appearing just before will help you:<br>
<br>
<b>Warning:</b> Cannot modify header information - headers already sent by (output started at script.php:X)<br>
<br>
It means that script.php outputs something at line X. Go to that line and fix it.
In case the message doesn't show, check if PHP warnings are enabled. If they are not,