Lots of script-driven applications, particularly paid cms, encode their files to ensure that they will not be reverse engineered or tampered with. The majority of them use an app called ionCube PHP Encoder to do this, so if you purchase a paid script and you want to set it up in a web hosting account, a software instrument called ionCube Loader needs to be present on your server. Without this, you won't be able to install the script or if you somehow manage to do that, it will not operate properly for the reason that most of the script code will be encrypted to a degree where it cannot be interpreted. In this light, you should make sure that ionCube Loader is present when you get a new website hosting account and you'd like to use some paid web application. If you buy a shared website hosting account and the instrument is not present, it can't be added as your entire server PHP environment shall have to be compiled again.