First verify that your Avisynth script text-file ends with extension".avs" and that the script file icon is the Avisynth icon 
. That means that Avisynth is properly installed and your text file is recognized as an Avisynth script by your operating system (BTW, what system is that?).
When all that is so, and a script "fails", the media player trying to show it will display an Avisynth error message. Did you get an error message? If so, what was it?