In August 2014, the server will be updated to continue to ensure the safety of all websites. A server upgrade, all software versions updated, and of course the PHP scripting language, which gets a new version (5.4).
Most sites with a CMS (Content Management System) use PHP, Joomla! as well uses PHP..
With Joomla! 1.5 and PHP 5.4 there problably will be no problems, but some extensions on these older sites (Joomla! 1.5) which have been installed, such as some Google Maps modules, event or calendar manager, could eventually display the error, or no longer work anymore with PHP 5.4.
Therefore, we strongly advise the migration of all websites made with Joomla! 1.5. Read more in this (German) article migrieren.