Server scheduled scripts have some major limits on what they can do and importing text from a network path is something it cannot do.
See this knowledge base article for more on the subject: http://help.filemaker.com/app/answers/detail/a_id/7035/p/874%2C953
You have two choices:
- Move the file to one of the few places where this server scheduled import works
- Use a robot file with an OS scheduler such as CRON or windows task scheduler to run this script from a client copy of filemaker pro.