Error 500 Ajax

Hi,

ich verwende in meinem Code ein Script, welches eine HTTP Anfrage an den serverseitigen Punkt sendet. Vom Grunde her findet der Server alles, was er braucht. Er gibt mir nur einen Error 500 zurück. Chrome DevTools gibt mir den Fehler bei
"xhr.send();"
Was könnte in diesem Fall das Problem sein?

hier der Code:

  <script>

        function getQuizData() {

            var xhr = new XMLHttpRequest();
            xhr.open('GET', 'get_questions.php', true);  
            xhr.onreadystatechange = function () {

                if (xhr.readyState === 4 && xhr.status === 200) {
                    var quizData = JSON.parse(xhr.responseText);
                    displayQuiz(quizData);
                }
            };
           xhr.send();
        }

        function displayQuiz(quizData) {

            var quizContainer = document.getElementById('quiz-container');  


            var randomQuestions = shuffleArray(quizData.questions).slice(0, 30);


            randomQuestions.forEach(function (question) {

                var questionElement = document.createElement('div');  

                questionElement.innerHTML = '<h3>' + question.question + '</h3>';  


                question.choices.forEach(function (choice) {

                    var choiceElement = document.createElement('input');  

                    choiceElement.type = 'radio';  

                    choiceElement.name = question.id;

                    choiceElement.value = choice;

                    questionElement.appendChild(choiceElement);

                    var labelElement = document.createElement('label');  

                    labelElement.innerHTML = choice;

                    questionElement.appendChild(labelElement);

                    questionElement.appendChild(document.createElement('br'));  

                });

                questionElement.addEventListener('change', function (event) {  
                    var selectedAnswer = event.target.value;
                   if (selectedAnswer === question.correctAnswer) {

                        alert('Richtige Antwort!');  

                    } else {

                        alert('Falsche Antwort!');  
                    }
                });
                quizContainer.appendChild(questionElement);

                quizContainer.appendChild(document.createElement('hr'));  

            });
        }

        function shuffleArray(array) {
           var currentIndex = array.length,
                temporaryValue,
                randomIndex;

            while (0 !== currentIndex) {
                randomIndex = Math.floor(Math.random() * currentIndex);
                currentIndex -= 1;

                temporaryValue = array[currentIndex];
                array[currentIndex] = array[randomIndex];
                array[randomIndex] = temporaryValue;
            }
            return array;
        }  
        getQuizData();

    </script>