Symfony 2 - Form errors - get error type

Yes you can. It's not a very clean way (since it's a pretty custom use case of forms), but it's possible.

Here's a simple code sample. It may not handle some edge cases, but works for my forms:

    //You can get errors from form like this:
    $errors = $form->getErrors(true);

    // Or like this if you want to check a particular field of your form
    $errors = $form->get('someField')->getErrors(true);

    //Now you have to iterate them and check 
    //if it's the error that you're looking for
    foreach($errors as $error) {
        //From the error you can get the constraint that caused it.
        $constraint = $error->getCause()->getConstraint();

        //Check if the constraint is the instace of the class
        //that you're insterested in.
        //It's ISBN validator in my example.
        if($constraint instanceof Symfony\Component\Validator\Constraints\Isbn) {
            // do anything you want.
            break;
        }

    }