A lot of script-driven apps, especially paid cms, encrypt their files so as to ensure that they will not be reverse engineered or tampered with. Many of them use an application called ionCube PHP Encoder to do this, so, in case you purchase a paid script and you want to install it in a web hosting account, an instrument called ionCube Loader has to be present on the server. Without this, you can't install the script or if you somehow find a way to do this, it will not operate effectively as most of the script code will be encoded to a degree where it can't be interpreted. That's why, you need to make sure that ionCube Loader is installed when you get a new website hosting account and you wish to use some paid web application. If you obtain a shared web hosting account and the tool is not present, it can't be added as your entire server PHP environment shall have to be compiled again.