If you are transferring older version of Magento to new servers or if you have upgraded your version of php to 5.3.3+ you will find some fatal errors while working with 1.3x versions of Magneto. There are 3 lines you will need to change in core code:

1) /lib/Varien/Object.php (Line 484)
replace __toString
with __invoke

2) /app/code/core/Mage/Core/Controller/Request/Http.php (Line 274)
replace split
with explode

3) app/code/core/Mage/Admin/Model/User.php (Line 374)
replace split
with explode