Duplicate Email Registration

[maivers]

I noticed a problem where returning customers weren't recognized when trying to login and I have narrowed the problem down to having duplicate accounts with the same email. I've been looking through store/catalog/create_account.php, it looks like this is the code that is supposed to check for duplicate emails. Not sure why it's not working. Any ideas would be much appreciated.

if (strlen($email_address) < ENTRY_EMAIL_ADDRESS_MIN_LENGTH) {
  $error = true;

  $messageStack->add('create_account', ENTRY_EMAIL_ADDRESS_ERROR);
} elseif (tep_validate_email($email_address) == false) {
  $error = true;

  $messageStack->add('create_account', ENTRY_EMAIL_ADDRESS_CHECK_ERROR);
} else {
  $check_email_query = tep_db_query("select count(*) as total from " . TABLE_CUSTOMERS . " where customers_email_address = '" . tep_db_input($email_address) . "'");
  $check_email = tep_db_fetch_array($check_email_query);
  if ($check_email['total'] > '0') {
	$error = true;

	$messageStack->add('create_account', ENTRY_EMAIL_ADDRESS_ERROR_EXISTS);
  }
}