What causes "Call to undefined function session_status ()"?

This response already was given in comment form and, As suggested , I'll be adding it as a response as well as better elaborate it with links and formatting.

session_status () is a feature introduced in PHP 5.4.

If a code with this function runs in any version lower than 5.4, it will be considered a function defined by the user which, because it has not been implemented and / or could not be automatically located, such as by include / require but error suppressed, this undefined function error is triggered.

As for the relationship with FileZilla , which is a mere FTP client for this case, it is the one who is intermuting the local file, which is probably running under a server on which PHP installed is version 5.4 or higher, with the server that must be 5.3 or lower.