PDO beginTransaction Not Letting Script Execute - php

Question

I have a PHP script using PDO Transactions.
$PDO->beginTransaction();
$sth = $PDO->prepare("INSERT INTO tbl_last_packing_upload (folderID, subfolderID) VALUES (1, 1)");
$sth->execute();
For some reason, this works locally (the INSERT runs), but not when I push it to my remote server.
To get my INSERT to work remotely, I need to put it ABOVE the $PDO->beginTransaction(); line. The following works remotely:
$sth = $PDO->prepare("INSERT INTO tbl_last_packing_upload (folderID, subfolderID) VALUES (1, 1)");
$sth->execute();
$PDO->beginTransaction();
Why does my INSERT not fire on my remote server when I have it placed inside the beginTransaction? I have many other PHP scripts on the same remote server using transactions and they all work fine.
Any ideas?

Answer 1

Unless there is an existing open transaction ($PDO->beginTransaction() was previously called but uncommitted), there should be no issue with the code as posted. If there was an open transaction, PDO would throw an exception when attempting to start a new one.
You already have PDO setup to throw exceptions rather than error silently with
$PDO->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
and if your transaction and INSERT statement code are wrapped in a try/catch block, you will need to debug and inspect the error caught in the catch block.
An error caught in catch (PDOException $e) {...} won't go into PHP's built-in error reporting mechanism on its own, so you'll need to force it to print to a location you can read. On a production web server, you won't want to print it to the screen, so instead I would recommend writing it to the web server's error log with PHP's error_log() function. A simple write to the default log location requires only the message as a parameter.
try {
// everything posted above
} catch (PDOException $e) {
// Caught an error, write it to the log
error_log("Error at line " . __LINE__ . " in " . __FILE__ . ": " . $e->getMessage());
// Whatever else you already do to handle the error...
// etc...
}