I doubt its something to do with your PHP code, that is probably working fine.
In your <FORM> tag did you remember to write method="POST"?
That was a well written post, giving us the relevant bits, it's very helpful for us to help you. But, could you explain more about what you mean by "will not let me"?
Also, this is not really related to what you want, but you will find your page would be more efficient if you merged it into just one query:
$selectSQL = 'SELECT * FROM yourtable WHERE id IN (' . implode($_POST['id'], ',') . ')';
$deleteSQL = 'DELETE FROM yourtable WHERE id IN (' . implode($_POST['id'], ',') . ')';
Using the IN function you can specify multiple ids to select/update or delete in a query. And having one query will be faster than having multiple. Hopefully this will improve the performance of your page.