致命错误：无法在PHP代码中使用函数返回值

Im Getting this Error Code, and can't understand why. The code hasn't been changed:

Fatal error: Can't use function return value in write context in /var/www/vhosts[...]

Code:

if ($this->edit_mode) {
            // Check if submission is genuine and not trying to change another entry
            $id = $form_data['id'];
            if (!is_numeric($id) || !isset($submissions[$id]) || $submissions[$id]['hash'] != $form_data['hash']) {
                echo '<p class="attention">'.sprintf(__('You have been about to submit a form of inconsistent state.', self::textdomain)).'</p>'."
";
                return false;
            }
            // Preserve some of the existing data which is not exposed in the edit form
            if (isset($submissions[$id]['note']))
                $form_data['note'] = $submissions[$id]['note'];
            $form_data['paid'] = $submissions[$id]['paid'];
            $form_data['date'] = $submissions[$id]['date'];
            $form_data['edit_date'] = date("Y-m-d H:i:s");

I can't figure out what the problem is! I would really appreciate some help. Thanks Guys!