If a DataGridView with a checkbox column can’t be checked verify whether editing has been
disabled. EditMode set to EditOnKeystrokeOrF2 appears to work OK.

To prevent editing of specific columns, use the CellBeginEdit event or set the ReadOnly property of the column.

private void dataGridView1_CellBeginEdit(object sender, DataGridViewCellCancelEventArgs e)
{
}

Also make sure the DataGridView is Enabled and not ReadOnly!