Problem parsing variables into sessions

I have set up a site where the user can register and login and that is all working correctly but I am having trouble parsing the session variable.

Here is the code

[code=php]
$_SESSION[‘username’] = Fred; // if I hard code it here and in functions.php it works but if I try to parse the username from the $username variable it won’t

eg

$_SESSION[‘username’] = $username doesn’t carry across

[/code]

The session start function is called from the config.php file so runs on every page.

What am I missing???

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