I updated the code on github so that it will give separate error messages.  Now, it will give an error if the filename is bad, and it will give a separate error if the pico can't open and send the file (usually caused when the file is too large).

I also added "led_website.html".  This demonstrates how to use XMLHttpRequest to set the LED on the raspberry pi pico, and has a timer that automatically queries the status of the LED to display on the website without having to refresh the page.