Data successfully inserted, yet execute() returns false

Question

I have searched here for answer to my problem. Some might had already answered here with other versions or drivers. This answer would help me a lot to go forward in my developments.

My PDOStatement::prepare() is returning true. But my PDOStatement::execute(); returning false.

Whereas, The rows are inserting successfully in the database. I have searched for the problem in php.net as well as PDO documentations. My search went in vein.

My simple insert code is as follows:

// get current rank into a variable //

$sql = 'SELECT count(email)+1 AS RANK FROM users_main';

$pre = $dbc->prepare($sql);

if($pre){

    $pre->execute(array($email)); // <-- working good ... 

    $res = $pre->fetchObject();

    if($res)$rank=(string)$res->RANK;else $rank='';
}   

// now inserting new user into the table as per his new rank.   

$usercode = substr(md5(gzencode($email)),0,10);
$activationcode = md5(gzencode(substr(md5($email),0,10)));


// inserting the actual row into db ... 

$sql = "INSERT INTO users_main(email,usercode,activation_code,current_rank) VALUES (?,?,?,?)";
$pre = $dbc->prepare($sql);


// debugging ... 
echo '<pre>';

try {   
    $pre->execute(array($email,$usercode,$activationcode,$rank));    // <-- PROBLEM IS HERE . RETURNING FALSE.  
}catch(Exception $e){   
    echo $e->getMessage();  // <--  NO ERROR MESSAGE    
}


echo '<br><br>';

print_r($dbc->errorInfo());    //   <-- here sqlstate is 0000

echo '</pre>';

    /*$emailSubject = 'Welcome Mail!';
    $emailLink = '?b='.$activationCode;
    if(insertEmailQueue('W',$email,$emailSubject,$emailLink))return true;else return false;
    }*/    

Adding to the above information, I have checked the datatype of each columns I am trying to insert into. Everything looks fine. Replying this question would really help me a lot.

UPDATE

I was debugging above code and I was trying to change to get what is the error. I have changed the code as below :

try {

    $res = $pre->execute(array($email,$usercode,$activationcode,$rank));    // <-- PROBLEM IS HERE . RETURNING FALSE.

}catch(PDOException $e){    
    echo $e->getMessage();  // <--  NO ERROR MESSAGE    
}


echo '<br><br>';

print_r($dbc->errorInfo());    //   <-- here sqlstate is 0000

echo '<br><br>';

print_r($dbc->errorCode());

echo '<br><br>';

print_r($pre->errorCode());

echo '</pre>';

The result was as below :

Array
(
    [0] => 00000
    [1] => 
    [2] => 
)


00000

23000    // <-- this is a fatal error as per the documentation.

Answer 1

After a two days long struggle to know what the error was, finally I found by trying to get error and other internet references. What I have changed is

    .... 

    // now inserting new user into the table as per his new rank.   

    $usercode = addslashes(substr(md5(gzencode($email)),0,10));
    $activationcode = addslashes(md5(gzencode(substr(md5($email),0,10))));


    ....

addslashes() is one of the primitive way to escape the unacceptable characters.

I still wonder, why did MySQL accept the statement, insert the rows and returned false after inserting. I will update the answer if I find out why this weird problem occurs.

Thank you every one for helping me.