C#

static class Program
    {
    /// <summary>
    /// The main entry point for the application.
    /// </summary>
    [STAThread]
    static void Main()
        {
        Application.EnableVisualStyles();
        Application.SetCompatibleTextRenderingDefault(false);
        Application.Run(new frmMain());
        }
    }

Quote:

If you attach to it, you should detach as well just in case of later changes.

string base64 = Convert.ToBase64String(file.ReadAllBytes(@"D:\Temp\myPicture.wmf"));

metfile = New Metafile(hdc, EmfType.EmfPlusDual)

Install-Package Newtonsoft.Json

JObject result = JObject.Parse(strsb);
bool isValid = (bool)result["valid"];

public class ResponseData
{
    public bool valid { get; set; }
    public IList<string> messages { get; set; }
    public string iban { get; set; }
    public BankData bankData { get; set; }
    public IDictionary<string, bool> checkResults { get; set; }
}

public class BankData
{
    public string bankCode { get; set; }
    public string name { get; set; }
}

...

var result = JsonConvert.DeserializeObject<ResponseData>(strsb);
bool isValid = result.valid;

{
  "valid": true,
  "messages": [],
  "iban": "DE...........",
  "bankData": {
    "bankCode": "",
    "name": ""
  },
  "checkResults": {}
}

• you're missing a reference to the assembly where the type is defined; or
• you're missing a using statement for the namespace where the type is defined; or
• you've got the wrong type name; or
• you haven't written the type.