The Sonic Pi file moonlightSonata-RF.rb which plays Beethoven's Moonlight Sonata 1st Movement requires the use of the Grand Piano samples from the Sonatina Symphonic Orchestra produced by Matthias Westlund.
Unfortunately this is no longer available from his website https://sso.mattiaswestlund.net/ However there is an alternative available at https://github.com/peastman/sso from where you can download the library. It is coverd by a https://creativecommons.org/licenses/sampling+/1.0/ Download and expand on your Desktop, or other suitable location and then set the link in the program at line 9 appropraitely for your installation.
The file should be run using the run_file "/path/to/file/location" command as it is too long to run from a Sonic Pi buffer.
An alternative version using the built in piano synth in Sonic Pi is included for comparison.