A lot of script-driven apps, especially paid cms, encode their files in order to make sure that they will not be reverse engineered or tampered with. Most of them use an app called ionCube PHP Encoder to do that, so if you buy a paid script and you would like to install it in a hosting account, a tool known as ionCube Loader needs to be present on your server. Without having it, you can't install the script or in case you somehow manage to do this, it will not work efficiently since almost all of the script code will be encoded to a point where it cannot be interpreted. That is why, you should make sure that ionCube Loader is installed when you get a new web hosting account and you want to take advantage of some paid web application. If you buy a shared hosting account and the instrument is not present, it cannot be added as your entire server PHP environment shall have to be compiled again.