SQL connection error from PHP after many operations

I'm currently looping to create a MBTiles map, and add information to my database each time. Here's how I configured my connection and execute actions during the loop:

if ($pdo_mbtiles == null) {
    echo "Opening new database connection".PHP_EOL;
    $pdo_mbtiles = new PDO('sqlite:'.$filename,
            '',
            '',
            array(
                PDO::ATTR_PERSISTENT => true
                )
            );
}
$pdo_mbtiles->setAttribute(PDO::ATTR_DEFAULT_FETCH_MODE, PDO::FETCH_ASSOC);
$pdo_mbtiles->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);

$q = $pdo_mbtiles->prepare("INSERT INTO tiles (zoom_level, tile_column, tile_row,tile_data) VALUES (:zoom_level, :tile_column, :tile_rowTMS, :tile_data)");
$q->bindParam(':zoom_level', $zoom_level);
$q->bindParam(':tile_column', $tile_column);
$q->bindParam(':tile_rowTMS', $tile_rowTMS);
$q->bindParam(':tile_data', $tile_data, PDO::PARAM_LOB);
$q->execute();

After 1018 times looping (this number doesn't change no matter how many times I try), I get this error message:

SQLSTATE[HY000]: General error: 14 unable to open database file

I checked the solution written here: How to prevent SQLITE SQLSTATE[HY000] [14]? but the echoed message only appears at the first time of the loop, so I assume the PDO connection isn't closed.

I didn't find other documentation relevant to this error code.

What could possibly go wrong here?

via Chebli Mohamed