[DonosOdD]

Update: it's ok now, I've solved it and it works perfectly.

The problem was indeed that variable, pcre.backtrack_limit. I changed my php.ini file to raise its value, but its local value was still at -1. Then I've found that there's a config file in the vbulletin installation called init.php, which has this line:

@ini_set('pcre.backtrack_limit', -1);

That was keeping the variable so low, and this is why code was always returning NULL.

I commented this line, and it began to work.

Well, guess that's it, hope I'm also able to help someone with this.

Cya!