CSS Switcher works local but not online

[MartinBurrito]

Hi there. I hope you guys can help :)

This works on local host but once online it fails with "PHP Warning:  session_start(): Cannot start session when headers already sent in /home/martinsb/public_html/switcher/switch.php on line 10"

Here is the nav  part

<!---new code added for style switcher-->
 
Style is set to <?php echo $_SESSION["msg"];?><br/>
      
        <a class="<?php echo $_SESSION['look0'];?>" href="switcher/switch.php?set=default">Default</a>
        <a class="<?php echo $_SESSION['look1'];?>" href="switcher/switch.php?set=ada">ADA</a>
        <a class="<?php echo $_SESSION['look2'];?>" href="switcher/switch.php?set=burrito">Burrito</a><br/>
        <div style="font-size:12px; padding-top:8px; padding-bottom:10px;"><?php echo $_SESSION["why"];?></div>
        

<!--end switcher-->

 

Here is the switcher.php

<?php

    $part= $_SERVER['HTTP_REFERER'];
    $path_parts = pathinfo($part);
     $result = $path_parts['basename'];
    
    
session_start();

?>
<?php
if( !isset($_GET['set'])){
    echo "";
    }
    
elseif ($_GET['set']=='default') {
        
        $_SESSION["css"]="css/mysite.css";
        $_SESSION["msg"]="Default";
        
        
        }    

elseif ($_GET['set']=='dark') {
        
        $_SESSION["css"]="css/darkstyles.css";
        $_SESSION["msg"]="Dark";
        
        
        }
        
elseif($_GET['set']=='light')  {
        
        $_SESSION["css"]="css/lightstyles.css";
        $_SESSION["msg"]="Light";
    
        
        }
        
if   ( !isset($_SESSION["css"]) )
    {$_SESSION["css"]="css/mysite.css";
        $_SESSION["msg"]="Default";
    
        }
        
        
        
?>    
<?php
// 301 Moved Permanently

header("Location: ../$result", true, 301);

exit();
?>

[requinix]

The error message says it's switch.php and that you're starting the session on line 10. That doesn't match up with what you've posted.