Got HTTP status 404 Not Found for "http://john-chambers.us/~jc/music/book/DftY/Thompson_24.abc/1792"
pngcmd="(./ps2png 512 512 /Users/jc/w/tmp/Tune-16554-1792.ps) >>/Users/jc/w/tmp/Tune-16554-get.log 2>&1" returned status 256
http://john-chambers.us/~jc/music/book/DftY/Thompson_24.abc/1792

Error exit status 256; here are some files to check:
[get.cgi V=1/1 B=0 scale=0.55 512x512 PNG]
filesizedescription
Coll_16554.log 452810 Log file, useful mostly for debugging
Tune-16554-1792.abc 153 ABC music file with the extracted tune(s)
Tune-16554-1792.ps 6 PostScript
Tune-16554-1792.txt 153 Plain-text file with the extracted tune(s)
Tune-16554-get.log 3981 Log file, useful mostly for debugging
These files should be available for 24 hours.