Has already more than 'max_user_connections' active connections

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

public partial class Photo_List : System.Web.UI.Page
{
    String connectionString = ConfigurationManager.ConnectionStrings["ConnStr"].ConnectionString;

    protected void Page_Load(object sender, EventArgs e)
    {

        Popola();
    }
    private void Popola()
    {
        OdbcConnection conn = new OdbcConnection(connectionString);
        string SQL = "SELECT * FROM photo where _category=?";
        conn.Open();
        OdbcCommand cmd = new OdbcCommand(SQL, conn);
        cmd.Parameters.AddWithValue("?", "" + Request.QueryString["PhotoCat"] + "");
        DataSet ds = new DataSet();
        OdbcDataAdapter da = new OdbcDataAdapter(cmd);
        da.Fill(ds);
        GridView1.DataSource = ds;
        GridView1.DataBind();
        da.Dispose();
        ds.Dispose();
        cmd.Dispose();
        conn.Close();
    }
    protected void GridView1_PageIndexChanging(object sender, GridViewPageEventArgs e)
    {
        GridView1.PageIndex = e.NewPageIndex;
        Popola();

    }
    protected void DropDownList1_Init(object sender, EventArgs e)
    {
        OdbcConnection conn = new OdbcConnection(connectionString);
        string SQL = "SELECT * FROM photo_category";
        conn.Open();
        OdbcCommand cmd = new OdbcCommand(SQL, conn);


        OdbcDataReader ddlValues;
        ddlValues = cmd.ExecuteReader();

        DropDownList1.DataSource = ddlValues;
        DropDownList1.DataValueField = "iCatId";
        DropDownList1.DataTextField = "cName";
        DropDownList1.DataBind();
        cmd.Dispose();
        conn.Close();
    }
    protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)
    {
        Response.Redirect("list.aspx?PhotoCat=" + DropDownList1.SelectedItem.Text + "");
    }
}