PHP Mailer responding with error 500. Help

Hey there guys. We use PHP mailer to send out and receive mail from our personal website. When we try using the form it gives us this error:

"/php/send_form_email.php:1 Failed to load resource: the server responded with a status of 500 (Internal Server Error)"

This is the code that is likely in question

    $mail->isSMTP();                                            // Send using SMTP
    $mail->Host       = 'smtp.zoho.com';                    // Set the SMTP server to send through
    $mail->SMTPAuth   = true;                                   // Enable SMTP authentication
    $mail->Username   = 'XXXXXXXX';                     // SMTP username
    $mail->Password   = 'XXXXXXXX';                               // SMTP password
    $mail->SMTPSecure = PHPMailer::ENCRYPTION_STARTTLS;         // Enable TLS encryption; `PHPMailer::ENCRYPTION_SMTPS` also accepted
    $mail->Port       = 587;                                    // TCP port to connect to

    $mailClient->isSMTP();                                            // Send using SMTP
    $mailClient->Host       = 'smtp.zoho.com';                    // Set the SMTP server to send through
    $mailClient->SMTPAuth   = true;                                   // Enable SMTP authentication
    $mailClient->Username   = 'XXXXXXXX';                     // SMTP username
    $mailClient->Password   = 'XXXXXXXX';                               // SMTP password
    $mailClient->SMTPSecure = PHPMailer::ENCRYPTION_STARTTLS;         // Enable TLS encryption; `PHPMailer::ENCRYPTION_SMTPS` also accepted
    $mailClient->Port       = 587;            