Lots of script-driven apps, particularly paid cms, encrypt their files to ensure that they will not be reverse engineered or tampered with. The majority of them use an application known as ionCube PHP Encoder to do that, so when you acquire a paid script and you'd like to install it in a website hosting account, a tool known as ionCube Loader has to be present on your server. Without it, you can't install the script or in case you somehow manage to do this, it won't work effectively for the reason that almost all of the script code will be encrypted to a degree where it cannot be interpreted. That is why, you have to ensure that ionCube Loader is present if you get a new hosting account and you'd like to use some paid web application. If you buy a shared web hosting account and the tool is not present, it can't be added because your entire server PHP environment will have to be compiled again.