Got HTTP status 404 Not Found for "http://john-chambers.us/~jc/music/book/DftY/Thompson.abc/1791"
pngcmd="(./ps2png 512 512 /Users/jc/w/tmp/Tune-26242-1791.ps) >>/Users/jc/w/tmp/Tune-26242-get.log 2>&1" returned status 256
http://john-chambers.us/~jc/music/book/DftY/Thompson.abc/1791

Error exit status 256; here are some files to check:
[get.cgi V=1/1 B=0 scale=0.55 512x512 PNG]
filesizedescription
Form_26242.log 860 Log file, useful mostly for debugging
Tune-26242-1791.abc 150 ABC music file with the extracted tune(s)
Tune-26242-1791.ps 6 PostScript
Tune-26242-1791.txt 150 Plain-text file with the extracted tune(s)
Tune-26242-get.log 3963 Log file, useful mostly for debugging
These files should be available for 24 hours.