I have commented out all references to sex_status and all seems to be fine now
// General data
$data['email'] = $email;
$data['name'] = $newsletter->normalize_name(stripslashes($_REQUEST['nn']));
$data['surname'] = $newsletter->normalize_name(stripslashes($_REQUEST['ns']));
// if ($options_profile['sex_status'] >= 1) {
// $data['sex'] = $_REQUEST['nx'][0];
// // Wrong data injection check
// if ($data['sex'] != 'm' && $data['sex'] != 'f' && $data['sex'] != 'n') {
// die('Wrong sex field');
// }
// }
// if ($options_profile['sex_status'] == 2) {
// $buffer .= "<!-- sex -->\n";
// $buffer .= "<tr>\n\t<th>" . $options_profile['sex'] . "</th>\n";
// $buffer .= "\t<td>\n\t" . '<select name="nx" class="newsletter-sex">' . "\n";
// $buffer .= "\t\t" . '<option value="m">' . $options_profile['sex_male'] . '</option>' . "\n";
// $buffer .= "\t\t" . '<option value="f">' . $options_profile['sex_female'] . '</option>' . "\n";
// $buffer .= "\t</select>\n\t</td></tr>\n";
// }
// if ($options_profile['sex_status'] == 2) {
// $buffer .= '<div class="newsletter-field newsletter-field-gender"><label>' . $options_profile['sex'] . '</label>';
// $buffer .= '<select name="nx" class="newsletter-sex">';
// $buffer .= '<option value="m">' . $options_profile['sex_male'] . '</option>';
// $buffer .= '<option value="f">' . $options_profile['sex_female'] . '</option>';
// $buffer .= '</select></div>';
// $buffer .= "\n";
// }
// if ($options['sex_status'] >= 1) {
// $buffer .= '<tr><th align="right">' . $options['sex'] . '</th><td><select name="nx" class="newsletter-sex">';
// // if (!empty($options['sex_none'])) {
// // $buffer .= '<option value="n"' . ($user->sex == 'n' ? ' selected' : '') . '>' . $options['sex_none'] . '</option>';
// // }
// $buffer .= '<option value="f"' . ($user->sex == 'f' ? ' selected' : '') . '>' . $options['sex_female'] . '</option>';
// $buffer .= '<option value="m"' . ($user->sex == 'm' ? ' selected' : '') . '>' . $options['sex_male'] . '</option>';
// $buffer .= '<option value="n"' . ($user->sex == 'n' ? ' selected' : '') . '>' . $options['sex_none'] . '</option>';
// $buffer .= '</select></td></tr>';
// }