Got HTTP status 404 Not Found for "http://john-chambers.us/~jc/music/book/CNS/Tune-73555-Book04.abc/tmp"
pngcmd="(./ps2png 512 512 /Users/jc/w/tmp/Tune-65521-tmp.ps) >>/Users/jc/w/tmp/Tune-65521-get.log 2>&1" returned status 256
http://john-chambers.us/~jc/music/book/CNS/Tune-73555-Book04.abc/tmp

Error exit status 256; here are some files to check:
[P=get.cgi V=1/1 B=0 scale=0.55 512x512 PNG]
filesizedescription
Tune-65521-get.log 4033 Log file, useful mostly for debugging
Tune-65521-tmp.abc 157 ABC music file with the extracted tune(s)
Tune-65521-tmp.ps 6 PostScript
Tune-65521-tmp.txt 157 Plain-text file with the extracted tune(s)
These files should be available for 24 hours.