Fatal error: Call to undefined function vtlib_purify()

Dear VTE Support Team,
i've just updated the VTE CRM from 441 to 45, but i've several problems:

1- On potentials.php I had a sintax error on row 825 ($queryGenerator->addConditionGlue($queryGenerator::$AND);) and i solved
it with $queryGenerator->addConditionGlue($queryGenerator->$AND);

2- i've a Fatal error: Call to undefined function vtlib_purify() on index.php on line 549; i try to fix it but i think there are some
problems with include file/function

If you can help me to fix all bugs for this version i will be very greatfull!

Best regards,
Lidia S

It's 5.2 version.
Anyway, you can look at the error at this URL
www.servizieditoriali.org/manager


Thank you! :)

Done, Upgraded to 5.3.x.
But the error is stil there. :(