В команде UPDATE
потеряйте круглые скобки. Вот и все.
Также, пожалуйста, остерегайтесь SQL-инъекций .
Обновление
Вот как должен выглядеть окончательный код:
function editAccount() {
$id = $_POST['id'];
$rep = $_POST['rep'];
$lastchange = date('mdY');
$account = $_POST['account'];
$areacode = $_POST['areacode'];
$number = $_POST['number'];
$address1 = $_POST['address1'];
$address2 = $_POST['address2'];
$city = $_POST['city'];
$state = $_POST['state'];
$zip = $_POST['zip'];
$country = $_POST['country'];
$fax = $_POST['fax'];
$descmaker1 = $_POST['descmaker1'];
$descmaker2 = $_POST['descmaker2'];
$title = $_POST['title'];
$email = $_POST['email'];
$cvendor = $_POST['cvendor'];
$cequipment = $_POST['cequipment'];
$leaseexp1 = $_POST['leaseexp1'];
$leaseexp2 = $_POST['leaseexp2'];
$leaseexp3 = $_POST['leaseexp3'];
$leaseexp4 = $_POST['leaseexp4'];
$leaseexp5 = $_POST['leaseexp5'];
$leaseexp6 = $_POST['leaseexp6'];
$volume = $_POST['volume'];
$notes = $_POST['notes'];
mysql_query("UPDATE accounts
SET lastchange = '$lastchange',
account = '$account',
areacode = '$areacode',
number = '$number',
address1 = '$address1',
address2 = '$address2',
city = '$city',
state = '$state',
zip = '$zip',
fax = '$fax',
descmaker1 = '$descmaker1',
descmaker2 = '$descmaker2',
title = '$title',
email = '$email',
cvendor = '$cvendor',
cequipment = '$cequipment',
leaseexp1 = '$leaseexp1',
leaseexp2 = '$leaseexp2',
leaseexp3 = '$leaseexp3',
leaseexp4 = '$leaseexp4',
leaseexp5 = '$leaseexp5',
leaseexp6 = '$leaseexp6',
volume = '$volume',
notes = '$notes'
WHERE id = $id");
}