Saving Opportunities (web ou API) causing HTTP 500

We are migrating an On Demand instance to On Site.

Almost everything seems to be OK, but we can't save Opportunities. Other modules work OK: Accounts, by example.

Everytime we try to save a new Opportunity (using Sugar interface or the API), a 500 Internal error occurs. The print screen of Sugar screen is attached.

Nothing is being logged neither in sugarcrm.log nor Apache error_log. But php_errors logs shows us something:

[25-Aug-2016 14:29:15 America/Sao_Paulo] PHP Fatal error: Call to undefined function bcadd() in /var/www/html/sugarcrm/include/SugarMath/SugarMath.php on line 310
[root@ip-172-18-2-31 /]# vim /var/www/html/sugarcrm/include/SugarMath/SugarMath.phpon bcdiv() in /var/www/html/sugarcrm/include/SugarMath/SugarMath.php on line 164

All file access, mod_rewrite and SELinux settings were verified and are OK.

What does this error means? Why would SugarMath.php file miss any method?

Tks!

[Update the post with the php_errors.log message. We were looking the wrong file.]