Thread:Extension talk:Scribunto/Error with scribunto/reply

As the error message says, PHP's proc_open function is not available in your environment. Most likely it is listed in PHP's "disable_functions" configuration directive.

If you have access to the PHP configuration, remove proc_open from disable_functions, or otherwise determine why proc_open is unavailable and fix it. If you do not have this access, you will have to discuss with your system administrator whether they can enable the function for you, or whether they would install the luasandbox PHP extension for you.