PHP stmt prepare fails but there are no errors

I had this same issue. The problem was that I was resusing the same mysqli connection with multiple prepared statements. After each execute statement, I was sure to include the explicit close command:

$stmt->close();

This stopped the error message being suppressed and I could then see the error message in $mysqli->error.

Here is a slightly adapted example script from php.net with error handling:

<?php
$mysqli = new mysqli("example.com", "user", "password", "database");
if ($mysqli->connect_errno) {
   echo "Failed to connect to MySQL: (" . $mysqli->connect_errno . ") " . $mysqli->connect_error;
}

/* Prepared statement, stage 1: prepare */
if (!($stmt = $mysqli->prepare("SELECT idDataSources FROM DataSources WHERE `description`=(?)"))) {
     echo "Prepare failed: (" . $mysqli->errno . ") " . $mysqli->error;
}

/* Prepared statement, stage 2: bind and execute */
$description = "File - 01/10/2015";
if (!$stmt->bind_param('s', $description)) {
    echo "Binding parameters failed: (" . $stmt->errno . ") " . $stmt->error;
}

if (!$stmt->execute()) {
    echo "Execute failed: (" . $stmt->errno . ") " . $stmt->error;
}

/* explicit close recommended */
$stmt->close();
?>

Please note that either $mysqli or $stmt can hold the error description.