One of the most common error found by the Joomla webmaster is "Direct access to this location is not allowed". The core reason for this error is that when we install Joomla or change it's template some modules and components of Joomla are not compatible with our existing Joomla website.
Lot of plugging, modules, components and templates developed for Joomla 1.0 version are incompatible with Joomla 1.5 version and vise versa.
By enabling the System - Legacy Plug-in the problem can be solved. For doing this follow the below steps.
Log in to your admin panel.
Go to Extensions -> Plugin Manager
Now enable the System - Legacy Plug-in from the Plug-in list.