How do I solve the System.BadImageFormatException error when creating an object?

Question

I'm building a student reputation management app in C#, but I get this error, I just created an object

System.BadImageFormatException. file or assembly'Library(namespace), Version=1.0.0.0, Culture=neutral, PublicKeyToken= 'null' or one of the files or assemblies that depend on it could not be loaded. An >attempt was made to load a program in the wrong format.

object:

    //class DBManager
    //Library Project(Print .dll)
    // Project Name:"Library"

        public class DBStudentsInfo
        {
            public int uid { get; set; }
            public string Name { get; set; }
            public string Number { get; set; }
            public string[] ManyPoints { get; set; }
            public string FinalPoint { get; set; }
            public string Memo { get; set; }
            public string Grade { get; set; }
        }

Project:Winform Custom Control

    using Library;
        //outher codes...

        public class Item
        {
            public DBManager.DBStudentsInfo SInfo = new DBManager.DBStudentsInfo();
        }

Project :Winform

    private void Form1_Load(object sender, EventArgs e)
        {
            UIListView.Item Aitem = new UIListView.Item(); // error got here
            uiListView1.AddItem(Aitem);
            uiListView1.AddItem(Aitem);
            uiListView1.AddItem(Aitem);
            uiListView1.AddItem(Aitem);
            uiListView1.AddItem(Aitem);
            uiListView1.AddItem(Aitem);
        }

.Net Framework Version = 4.7.2