App_Code files are ignored (Microsoft Visual Web Developer 2010 error)

I have a 'Connection.cs' file in the App_Code folder of Microsoft Visual Web Developer 2010, but it alerts me of an error:

The type or namespace name 'Connection' could not be found (are you missing a using directive or an assembly reference?)

('Connection' is the name of a class in the Connection.cs file)

I don't know much about referring files, and I didn't understand the error help description in MSDN. How can I fix it?

Edit:

The Connection.cs file:

public class Connection
{
    public void Insert(OleDbConnection cnctn, string tableName, string[] inputs, char[] types)
    {
        // new OleDbConnection(@"Provider=Microsoft.Jet.OleDb.4.0; Data Source=" + this.dbPath);

        string sql = "INSERT INTO " + tableName + " VALUES (";
        for (int i = 0; i < inputs.Length - 1; i++)
            sql += "@p" + i + ",";
        sql += "@p" + (inputs.Length - 1) + ")";

        cnctn.Open();
        OleDbCommand cmnd = new OleDbCommand(sql, cnctn);

        for (int i = 0; i < inputs.Length; i++)
        {
            if (types[i] == 'c')
                cmnd.Parameters.Add("@p" + i, OleDbType.VarChar);
            else if (types[i] == 'n')
                cmnd.Parameters.Add("@p" + i, OleDbType.VarNumeric);
            cmnd.Parameters["@p" + i].Value = inputs[i];
        }

        cmnd.ExecuteNonQuery();
    }

    public bool DoesExists(OleDbConnection cnctn, string tableName, string condition)
    {
        // new OleDbConnection(@"Provider=Microsoft.Jet.OleDb.4.0; Data Source=" + this.dbPath);
        cnctn.Open();
        OleDbCommand cmnd = new OleDbCommand("SELECT * FROM " + tableName + " WHERE " + condition, cnctn);
        bool temp = cmnd.ExecuteReader().Read();
        cnctn.Close();
        return temp;
    }

    public DataSet SetDataSet(OleDbConnection cnctn, string tableName, string sql)
    {
        cnctn.Open();
        DataSet ds = new DataSet();
        OleDbCommand cmnd = new OleDbCommand(sql, cnctn);
        OleDbDataAdapter da = new OleDbDataAdapter(cmnd);
        da.Fill(ds, tableName);
        cnctn.Close();
        return ds;
    }

    public void Execute(OleDbConnection cnctn, string sql)
    {
        cnctn.Open();
        OleDbCommand cmnd = new OleDbCommand(sql, cnctn);
        cmnd.ExecuteNonQuery();
        cnctn.Close();
    }
}

One of the files that uses this class:

public partial class register : System.Web.UI.Page
{
    private string[] errors = new string[5];
    protected void Page_Load(object sender, EventArgs e)
    {
        if (Request.Form["submit"] != nu开发者_JAVA百科ll)
        {
            string[] inputs = { 
                Request.Form["userName"],
                Request.Form["names"],
                Request.Form["password"],
                Request.Form["email"],
                Request.Form["birthDate"]
            };
            string[] regexString = {
                @"[^&<>\n]+( [^&<>\n]+)*",
                @"['\-A-z]{2,}( ['\-A-z]{2,})+",
                ".{5,}",
                @"\w+@\w+(\.\w+)+",
                @"(\d{4}-\d\d-\d\d)?"
            };
            char[] types = { 'u', 'i', 'i', 'i', 'd' };
            bool flag = true;
            OleDbConnection cnct = new OleDbConnection(@"Provider=Microsoft.Jet.OleDb.4.0; Data Source=" + Server.MapPath("App_Data/WMUdb.accdb"));
            for (int i = 0; i < inputs.Length; i++)
            {
                if (!(new Validation(inputs[i], regexString[i], types[i], cnct, "members").isValid()))//this is another class frome the App_Code, with the same problem.
                {
                    //error alert
                    flag = false;
                }
            }
            if (flag)
            {
                string[] values = new string[6];
                for (int i = 0; i < inputs.Length - 1; i++)
                    values[i] = inputs[i];
                values[5] = "1";
                Connection cnctn = new Connection();
                cnctn.Insert(cnct, "members", values, new char[6] { 'c', 'c', 'c', 'c', 'c', 'n' });

                Session["userName"] = inputs[0];
                Session["adminLevel"] = 1;
                Response.Redirect("homepage.aspx");
            }
        }
    }
}

2nd Edit:

I should mention that the App_Code file wasn't created automatically when I created the project, but add manually - I used "Add Item..." to create a folder with that name, added "Connection.cs" to it and that's it.

Use namespaces, Luke!

(for both files is the best case)