A Task Management System using Three Layer Architecture

using System;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;

public partial class UI_CreateProject : System.Web.UI.Page
{
    DataExecuteClass DEC = null;
    protected void Page_Load(object sender, EventArgs e)
    {
        string userId = Session["userId"].ToString();
        string userRole = Session["userRole"].ToString();
        this.Master.userId = userId;
        this.Master.UserRole = userRole;

       this.GenerateProjectId();
    }
    private void GenerateProjectId()
    {
        DEC = new DataExecuteClass();
        string countProject = "SELECT COUNT(*) FROM t_Project";
        object o = DEC.getSingleValue(countProject);
        int counter = int.Parse(o.ToString())+1;
        string n=null;
        if (counter < 10)
        {
            n = "00" + counter.ToString();
        }
        if (counter < 100 && counter > 9)
        {
            n = "0"+ counter.ToString();
        }
        if (counter > 99 && counter < 1000)
        {
            n = counter.ToString();
        }
        string projectId = "PRO-" + DateTime.Now.Year+"-"+n;
        projectIdTextBox.Text = projectId;

    }
    protected void createProjectButton_Click(object sender, EventArgs e)
    {
        ProjectBLL project = new ProjectBLL();
        //string projectAdmin = Request.QueryString["userId"].ToString();
        string projectAdmin = "fahmina90";
        Project projectObj = new Project(projectIdTextBox.Text, projectNameTextBox.Text, projectDescriptionTextBox.Text, projectClientTextBox.Text, creationDateTextBox.Text, endDateTextBox.Text, projectAdmin);
        string UserRole = "Admin";
        ProjectDetails ProjectDetailsObj = new ProjectDetails(projectIdTextBox.Text, projectAdmin, UserRole, creationDateTextBox.Text, endDateTextBox.Text);
        project.AddUserToProject(ProjectDetailsObj);
        int countUser = CheckBoxList1.Items.Count;
        for (int i = 0; i < countUser; i++)
        {
            if (CheckBoxList1.Items[i].Selected)
            {
                string userId = CheckBoxList1.Items[i].ToString();
                string userRole="User";
                ProjectDetails projectDetailsObj = new ProjectDetails(projectIdTextBox.Text, userId, userRole, creationDateTextBox.Text, endDateTextBox.Text);
                project.AddUserToProject(projectDetailsObj);
            }
        }
        string msg = project.AddNewProject(projectObj);
        Response.Redirect("CreateProject.aspx");

    }
}