are you doing something like this:
/******** ADD USER **********/
$user = "I'm a PHP developer";
/add slashes to make the string kosher for PHP & SQL*/
$user = addslashes($user);
mysql_db_query("database","INSERT INTO table SET user = '$user'");
use something similiar to retreive the user.
also be sure the username is in the table
and is what you expect it to be.