[TYPO3-dev] Error mod_fcgid on moving to new server

[lebond007]

Hello, 
I'm new to typo3, I'm sorry if I'm asking this question on the wrong part of this forum.

I'm trying to move a typo3 website from an old server to a new server.
Typo Version is 6.2.14.

When I move the website to the new server I get this error:
mod_fcgid: stderr: PHP Fatal error: Class 'Helhum\\ClassAliasLoader\\Composer\\ClassAliasLoader' not found in /var/www/vhosts/rational.it/httpdocs/typo3/contrib/vendor/autoload.php on line 14
 
Server administrator tells me it's a CMS problem.
Php version I'm using is 5.5. 
On the old server the website works so I don't understand what could be the problem.

Any help?

Thank you