Trouble getting value from dropdownlist

: Input string was not in a correct format

m.venueID = Convert.ToInt32(ddlvenue.SelectedValue);

public class MEETING
{
        private int MeetingID;
        private int VenueID;
        private string Venue;
        private string MeetingName;
        private DateTime MeetingStartDate;
        private DateTime MeetingEndDate;

        public int meetingID 
        {
            get { return MeetingID; }
            set { MeetingID=value;}
        }
        public int venueID 
        {
            get { return VenueID; }
            set { VenueID=value;}
        }
        public string meetingName 
        {
            get { return MeetingName; }
            set { MeetingName=value;}
        }
        public DateTime meetingStartDate
        {
            get { return MeetingStartDate; }
            set { MeetingStartDate=value;}
        }
        public DateTime meetingEndDate 
        {
            get { return MeetingEndDate;}
            set { MeetingEndDate=value;}
        }
        public string venue
        {
            get { return Venue; }
            set { Venue = value; }
        }
    }

protected void btnMeetings_Click(object sender, EventArgs e)
{
    MEETING m = new MEETING();

    try
    {
        m.meetingName = tbMeetingName.Text.ToString();
        m.venueID = Convert.ToInt32(ddlvenue.SelectedValue);
        m.meetingStartDate = Convert.ToDateTime(datePickerStart.Text); ;
        m.meetingEndDate = Convert.ToDateTime(datePickerEnd.Text);


        BusinessLogicLayer bl = new BusinessLogicLayer();
        try
        {
            //Popup label onga
            lblResult.Visible = true;
            lblResult.Text = "Added Succesfully";
            if (bl.AddMeeting(m) == true)
            {
                lblResult.Text = "Meeting was added successfully";

                Response.Redirect("WebForm14.aspx");
            }
        }
        catch (Exception exc)
        {
            lblResult.Visible = true;
            lblResult.Text = "";
            lblResult.Text = lblResult.Text + exc.ToString();
        }
    }
    catch (Exception exc)
    {
        lblResult.Visible = true;
        lblResult.Text = "";
        lblResult.Text = lblResult.Text + exc.ToString();
    }


}