Lots of script-driven apps, particularly paid cms, encode their files to make sure that they will not be reverse engineered or tampered with. Most of them use an application named ionCube PHP Encoder to do that, so if you purchase a paid script and you would like to install it in a hosting account, a software instrument called ionCube Loader has to be present on your server. Without it, you won't be able to install the script or in case you somehow manage to do that, it won't work efficiently for the reason that most of the script code will be encoded to a point where it cannot be interpreted. In this light, you have to ensure that ionCube Loader is present if you get a fresh web hosting account and you wish to use some paid web application. If you obtain a shared hosting account and the instrument is not present, it cannot be added because the whole server PHP environment shall have to be compiled again.