Theme Blurry Contact Form problems

My Contact Form doesn’t work.

I get the following message:
“We cannot verify that you are trying to send an email from this form. Please try again.”

Folder: contac-form
Filename: kontakt.php
Encoding: Unicode (UTF-8)

Page Inspector settings seemed in the right way:
Send To: EMail adress is OK
From Name: Your Name
From Email: Your Email
Subject: Subject
Required: Fields marked with *…
Symbol: *
Submit Button: Submit
Reset Button: Reset

What’s wrong? Who can help me?
ThanX in advance M

Some more information to this item above:
My DomaiServer is working with PHP 5.6.
Domain ErrorLog: "There is no wrong access in the last fiew days

Hi Mat, what’s your hosting provider? That would help to know.

ThanX for contacting me / the provider is a german one: STRATO / They offer php 5.3; 5.6; 7 / Regards Mat Grimm

You could try this fix, maybe it works for you:

The problem resists and I have alreadyno idea, what is the error:
The Domainservers Error-Logfile shows the following error message:
17.12.2016 02:11:32 [client] PHP Warning: session_start(): Cannot send session cache limiter - headers already sent (output started at /mnt/web018/b1/48/57617748/htdocs/contact-form/kontakt.php:1) in /mnt/web018/b1/48/57617748/htdocs/contact-form/kontakt.php on line 3, referer:

The kontakt.php begin is:

<?php // Start session. session_start(); // Set a key, checked in mailer, prevents against spammers trying to hijack the mailer. $security_token = $_SESSION['security_token'] = uniqid(rand()); if ( ! isset($_SESSION['formMessage'])) { $_SESSION['formMessage'] = 'Für Fragen stehen wir gerne für Sie bereit. Bitte füllen Sie das Kontaktformular aus und senden Sie uns Ihr Anliegen. Die Felder mit * sind notwendige Einträge.'; } if ( ! isset($_SESSION['formFooter'])) { $_SESSION['formFooter'] = ''; } if ( ! isset($_SESSION['form'])) { $_SESSION['form'] = array(); } function check($field, $type = '', $value = '') { $string = ""; if (isset($_SESSION['form'][$field])) { switch($type) { case 'checkbox': $string = 'checked="checked"'; break; case 'radio': if($_SESSION['form'][$field] === $value) { $string = 'checked="checked"'; } break; case 'select': if($_SESSION['form'][$field] === $value) { $string = 'selected="selected"'; } break; default: $string = $_SESSION['form'][$field]; } } return $string; } ?>

I see the URL for sending mail exist.
What’s wrong in the configuration?
ThanX in advance
Mat Grimm, Berlin