Constraint Violation when INSERT

Hi all,

I got the error " Constraint Violation " when I did an "INSERT" .
Gone thru the code umpteen times but to no avail..Wondering where my error
was??...Below is a snip of the block of code:

----------------------------------------------------
<?
$dsn = "mysql://root:**********@localhost/tablename";

$db = DB::connect ($dsn);
if (DB::isError ($db))
die ($db->getMessage());


//create variables ready to go into DB

$tutor_name = $db->quote($_POST["tutor_name"]);
$tutor_contact = $db->quote($_POST["tutor_contact"]);
$tutor_email = $db->quote($_POST["tutor_email"]);
$tutor_profile = $db->quote($_POST["tutor_profile"]);


$sql = "INSERT INTO tutor (tutor_name, tutor_contact, tutor_email,
tutor_profile)
VALUES ($tutor_name,$tutor_contact,$tutor_email,$tutor_pr ofile)";


$result = $db->query($sql);
if( DB::isError($result) ) {
die ($result->getMessage());
}
?>

-----------------------------------------------------------------------
Everything was fine and the "INSERT" works, user input was insert into the
database successful using the same block of code but the next thing i know I
got this error ....anyone know watz the proz here???
Hope to get some help soon. Thanks in advance=)

Irin.