C#. Populating DataGridView with data from database. Cant edit any rows, and Read Only is false

So i can't edit any columns in the DGV. Even when i set ReadOnly to 'False'. Some of my columns i don't want the users to edit the data but i want to be able to select the checkbox and i cant :(.. When i was debugging my code any of the columns i have set to ReadOnly = 'True' they are still coming accross as 'False' but i still cant click or edit anything!! Any tips on how to get around this? Spent far to long on this silly problem :(

So i want to just be able to tick the CheckBox, and i cannot do this for some reason.

            sqlConnection.Open();
            MessageBox.Show("Database " + strDatabase + " opened 
            successfully.");

            string sqlSelectCompanies = "SELECT data, moreData,  moreData1, moreData2 " +
                                        "FROM tblClient INNER JOIN tbl ON tbl = tbl WHERE Serverid >=1"); //I cant show all details of the query
            SqlCommand sqlCommand = new SqlCommand(sqlSelectCompanies, sqlConnection);
            SqlDataAdapter sqlDataAdapter = new SqlDataAdapter(sqlCommand);
            sqlDataAdapter.Fill(companyDataSet, "Companies");
            dataGridViewCompanies.DataSource = companyDataSet;
            dataGridViewCompanies.DataMember = "Companies";
            dataGridViewCompanies.ReadOnly = true;
            //dataGridViewCompanies.Columns[0].ReadOnly = true;
            //dataGridViewCompanies.Columns[1].ReadOnly = true;
            //dataGridViewCompanies.Columns[2].ReadOnly = true;
            //dataGridViewCompanies.Columns[3].ReadOnly = true;

            //Enabling multiple row selection
            dataGridViewCompanies.MultiSelect = true;
            dataGridViewCompanies.SelectionMode = 
            GridViewSelectionMode.FullRowSelect;

            this.dataGridViewCompanies.AllowSearchRow = true;
            dataGridViewCompanies.AutoSizeColumnsMode = GridViewAutoSizeColumnsMode.Fill;
            dataGridViewCompanies.EnableGrouping = false;

            GridViewCheckBoxColumn gvCheck = new GridViewCheckBoxColumn();
            gvCheck.Name = "Select Company";
            dataGridViewCompanies.MasterTemplate.Columns.Add(gvCheck);
            dataGridViewCompanies.Columns[4].HeaderText = "Select Company";
            //dataGridViewCompanies.MasterTemplate.Columns[4].ReadOnly = false;
            //dataGridViewCompanies.Columns[4].OwnerTemplate.AllowEditRow = true;
            dataGridViewCompanies.Columns[4].ReadOnly = false;