Please provide more detail of the error you are receiving. What specific sensor are you using, how are you interfacing it to the Galileo? Have you downloaded any additional libraries, how have you installed them? Are you using an IDE o Linux console? What image are you using? What code are you using, what is the complete error log?
What RFID module are you using? Different modules might have different ways of connecting; do you have the module’s datasheet?