ASP.Net with SQL Server Express 2008

protected void btnSubmit_Click(object sender, EventArgs e)
        {
            try
            {
                string connStr = @"Data Source=.\SQLEXPRESS;AttachDbFilename=D:\MyProjects\LeaveMgt\LeaveMgt\App_Data\LeaveMgt.mdf;Integrated Security=True;User Instance=True";
                SqlConnection dbCon = new SqlConnection(connStr);
                SqlCommand comm = new SqlCommand();
                dbCon.Open();
                comm.CommandType = CommandType.Text;
                comm.Connection = dbCon;
                comm.CommandText = ("INSERT INTO LeaveCover VALUES('" + txtEmpNo.Text + "','" + txtEmpName.Text + "','" + txtCoverUp.Text + "','" + txtActOff.Text + "', '" + txtDate.Text + "','" + txtLevAdd.Text + "','" + ddlApprove.Text + "', '" + ddlNor.Text + "','" + ddlNotLev.Text + "')");
                comm.ExecuteNonQuery();
                dbCon.Close();
                lblMessage.Text = "Ok";
            }
            catch {

                lblMessage.Text = "Bad";
            
            }

When I click the submit button it always trig the cath{} but I cannot find the error!
My Database is at the following location and the connection string is as the following.

DB@ <pre lang="c#">D:\MyProjects\LeaveMgt\LeaveMgt\App_Data\LeaveMgt.mdf

string connStr = @"Data Source=.\SQLEXPRESS;AttachDbFilename=D:\MyProjects\LeaveMgt\LeaveMgt\App_Data\LeaveMgt.mdf;Integrated Security=True;User Instance=True";