Delete the selected datas from database with checboxes

I have solved porblem using the dataGridView1.Rows[j].Cells[1].Value instead of dataGridView1.Rows[j].Cells["gid"].Value

Thanks for your intrest.

Yes. that was I mentioned. Please review thorougly this column.  The same column you are trying to use for deleting a record. 

if (Convert.ToBoolean(dataGridView1.Rows[i].Cells["gid"].Value) == true) .  You are converting the column dataGridView1.Rows[i].Cells["gid"].Value to boolean and the same column you have used in delete query which I got confused. 

Thanks for your intrest Prasad but the result is same. I am getting this error in this line.

System.FormatException: 'Dize geçerli bir Boole deger olarak taninmadi.'

Please cross check whether the key value which you are sending to script is valid.

dataGridView1.Rows[j].Cells["gid"].Value

check the below code

int i = 0;
List ChkedRow = new List();

for (i = 0; i <= dataGridView1.RowCount - 1; i++)
{
    if (Convert.ToBoolean(dataGridView1.Rows[i].Cells["gid"].Value) == true)
    {
        ChkedRow.Add(i);
    }
}

if (ChkedRow.Count == 0)
{
    MessageBox.Show("En az bir checkbox seçiniz!");
    return;
}

foreach (int j in ChkedRow)
{
    try
    {
        using (OleDbConnection conn = new OleDbConnection(connectionString))
        {
            conn.Open();

            string cmdText = "DELETE FROM gezilistemiz25 WHERE gid = ?";
            OleDbCommand command = new OleDbCommand(cmdText, conn);
            command.Parameters.AddWithValue("gid", dataGridView1.Rows[j].Cells["gid"].Value);
            command.ExecuteNonQuery();
        }
    }
    catch (Exception ex)
    {
        MessageBox.Show(ex.Message, "Error", MessageBoxButtons.OK, MessageBoxIcon.Error);
    }
}

MessageBox.Show("Kayitlar basariyla eklendi!");