Flow cli throws class not found error migrating to Neos 3.0

Hi,
I was tryinh to follow the migration guid to Neos 3.0 but I got stuck at “try if ./flow command works” step.
I got this error with no System_Development.log trace:

Fatal error: Uncaught Error: Class 'Neos\Error\Messages\ErrorHandler' not found in /var/www/Packages/Framework/Neos.Flow/Classes/Core/Booting/Scripts.php:265
Stack trace:
#0 [internal function]: Neos\Flow\Core\Booting\Scripts::initializeErrorHandling(Object(Neos\Flow\Core\Bootstrap))
#1 /var/www/Packages/Framework/Neos.Flow/Classes/Core/Booting/Step.php(52): call_user_func(Array, Object(Neos\Flow\Core\Bootstrap))
#2 /var/www/Packages/Framework/Neos.Flow/Classes/Core/Booting/Sequence.php(107): Neos\Flow\Core\Booting\Step->__invoke(Object(Neos\Flow\Core\Bootstrap))
#3 /var/www/Packages/Framework/Neos.Flow/Classes/Core/Booting/Sequence.php(111): Neos\Flow\Core\Booting\Sequence->invokeStep(Object(Neos\Flow\Core\Booting\Step), Object(Neos\Flow\Core\Bootstrap))
#4 /var/www/Packages/Framework/Neos.Flow/Classes/Core/Booting/Sequence.php(111): Neos\Flow\Core\Booting\Sequence->invokeStep(Object(Neos\Flow\Core\Booting\Step), Object(Neos\Flow\Core\Bootstrap))
#5 /var/www/Packages/Framework/Neos.Flow/Classes/Core/Booting/Sequence.php( in /var/www/Packages/Framework/Neos.Flow/Classes/Core/Booting/Scripts.php on line 265

I removed any custom or additional packages (with the idea of addding them back later one-by-one) to make it simpler and cleaner but I can’t get through this.

Any ideas?

Funny thing flow setpermissions command seems to work just fine, at least does not throw any error, while help does tough.

Thank you for your always great help,
Nicola