...
BindingSource m_binding;
...
da = new SqlDataAdapter(@"   SELECT  firm, user, adress
                                                      FROM USERS", conn);
                ds = new DataSet();
                da.Fill(ds);
                
                m_binding  = new BindingSource();
                dataGridView1.DataSource = m_binding;
                m_binding.DataSource = ds.Tables[0].DefaultView;

...
protected void ComboBox1_SelectedValueChanged(object sender, EventArgs e)
{
   m_binding.Filter = string.Format("type like '%{0}%'",ComboBox1.SelectedValue);
}
...