Apache + php + htaccess fix on Debian

A website have been moved from a server to another, but it is not working due to some difference in folder config, unix permissions, and a htaccess combined with a custom PHP framework. In example it uses Smarty version 2.6.20 that do not render anything to its cache. The previous version still runs on PHP 5.2 vs 5.4 in the new. PHP code is very simple, with 123 files, anyway strong PHP skills will be required. attached the htaccess file