System.TypeAccessException: Attempt by method ‘X’ to access type ‘Y’ failed

Ok, I have googled this for almost two days and I have tried almost all SO solutions that are related to this error, but nothing works. And most questions about this are for Security ssettings on Click-once applications, JSON, web applications etc. But nothing for a plain old winforms app.

Here is the full error

System.TypeAccessException: Attempt by method ‘Microsoft.Xml.Serialization.GeneratedAssembly.XmlSerializationWriterSystemSetup.Write3_SystemSetup(System.Object)’ to access type ‘DataFacture.Common.Globals+SystemSetup’ failed.
at Microsoft.Xml.Serialization.GeneratedAssembly.XmlSerializationWriterSystemSetup.Write3_SystemSetup(Object o)

Here is a simplified version of the’SystemSetup’ class

public class SystemSetup
        private string machineId, windowsVersion;

        public SystemSetup() { }
        public SystemSetup(string machineId, string windowsVersion)
            this.machineId = machineId;
            this.windowsVersion = windowsVersion

        public string MachineID { get { return machineId; } set { machineId = value; } }
        public string WindowsVersion{ get { return windowsVersion; } set { windowsVersion= value; } }

Now I’m trying to generate an XML of a SystemSetup object using the following code, and at the ‘writer.Serialize(wfile, objectSerializer);’ line, the error occurs

public static void WriteXML(Object objectSerializer, String XMLPath, String FileName)
            if (XMLPath.Substring(XMLPath.Length - 1, 1) != @"/")
                XMLPath = String.Format("{0}", XMLPath);

            XmlSerializer writer = null;
            Type objectType = objectSerializer.GetType();
            switch (objectType.Name)
                case "SystemSetup":
                    writer = new XmlSerializer(typeof(Globals.SystemSetup));

            var wfile = new System.IO.StreamWriter(String.Format("{0}{1}", XMLPath, FileName));
            writer.Serialize(wfile, objectSerializer);
        catch (Exception ex)

This is a winforms applications. It is not click once. And I have not enforced any security restrictions on any assembly. Also, there are no 3rd party assemblies that I’m calling from here.

Source: .net

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