Legacy Php Application

I just migrated a legacy php application to a new computer running on Centos 7 with Php 5.4 and Mariadb 5.5 due to the old hardware (Centos 5 with Php 5.2.14 and Mysql 5.1.51) dying. I am getting php fatal error when writing to a table (PHP Fatal error: Call to a member function execute() on a non-object in database_handler.php on line 42). This only happens when I am trying to update or create new records in only these two tables. I do not have any issues updating or inserting records in other tables. When I connect the php application to a remote database running on the something like the old server specification, it works fine for that two tables. Can someone shed some light on the error? Is it due to Php version or Mariadb version? Do I need to upgrade the Smarty version or I can just do something (edit) to the existing code. The legacy php application is written using Smarty 2.6.26. Any advice is greatly appreciated. Thank you.