An AccessViolationException error appears: "An attempt was made to read or write to protected memory." What could be the problem?

Question

API

What is the point: it was necessary to make a drop-down list of users (combobox). After a user is selected from the list, he is added to a certain file, then the combobox'a field is again free for input.
Implementation: In the field combobox'a begin to enter the full name, a drop-down list appears with users whose full name matches the entered. The search for matches is implemented through a request to the server API (using JIRA), then the resulting list is processed and stored in an array, then this list is displayed in the combobox.
Problem: sometimes the code works stably, but it happens that after every 4-5 requests an AccessViolationException error appears "An attempt was made to read or write to protected memory. This often indicates that other memory is corrupted."
I would like to fix this problem. Previously, the error appeared more often, I thought that the server was blocking frequent calls, so the request was sent every 4 characters. After that, the problem was forgotten until the program was used in normal operating mode.

public void dropDownList(ComboBox comboBox)
        {
            comboBox.Text = comboBox.Text;
            string text = comboBox.Text;

            string url = "https://serverAddress/api/2/user/picker?maxResults=7&query=" + text;

            HttpWebRequest request = (HttpWebRequest)WebRequest.Create(url);

            request.CookieContainer = new CookieContainer();
            request.Method = "GET";
            request.ContentType = "application/json; charset=utf-8";
            request.CookieContainer.Add(Session.cookies);
            try
            {
                using (HttpWebResponse response = (HttpWebResponse)request.GetResponse())
                {
                    Stream stream = response.GetResponseStream();
                    JsonSerializer jsonSerializer = new JsonSerializer();

                    using (StreamReader reader = new StreamReader(stream))
                    {
                        using (JsonTextReader jsonTextReader = new JsonTextReader(reader))
                        {
                            var obj = jsonSerializer.Deserialize(jsonTextReader);
                            string jsonString = @JsonConvert.SerializeObject(obj);

                            JObject jObject = JObject.Parse(jsonString);
                            JArray array = (JArray)jObject["users"];
                            comboBox.Items.Clear();
                            comboBox.SelectionStart = text.Length;
                            int count = array.Count;
                            userArray = new string[count];
                            string temp = "";

                            for (int i = 0; i < count; i++)
                            {
                                temp = string.Format("{0}", array[i]["html"]);
                                temp = temp.Replace("strong>", "").Replace("<", "").Replace("/", "");
                                userArray[i] = temp;
                                temp = "";
                            }

                            comboBox.Items.AddRange(userArray);
                            Array.Clear(userArray, 0, count);
                        }
                    }


                }
            }
            catch 
            {
                MessageBox.Show("Что-то пошло не так");
            }
        }

Answer 1

This error can only occur in unmanaged code.
PS: what version of the framework? In 4th SEH exceptions are not caught by default.

Answer 2

1. In "AssemblyInfo.cs" you need to add:
2. Instead of:

catch
{
    MessageBox.Show("Что-то пошло не так");
}

better to do:

catch (Exception ex)
{
    Debug.WriteLine(ex);
    MessageBox.Show(ex.Message);
}

As a result, you will get a detailed description, as well as an indication of the source of the problem (see the output window in the debugger).
PS I would venture to suggest that the guys from NewtonSoft coded the code.