Got HTTP status 404 Not Found for "http://john-chambers.us/~jc/music/book/1804/cont.abc"
pngcmd="(./ps2png 512 512 /Users/jc/w/tmp/Tune-51939-cont.ps) >>/Users/jc/w/tmp/Tune-51939-get.log 2>&1" returned status 256
http://john-chambers.us/~jc/music/book/1804/cont.abc

Error exit status 256; here are some files to check:
[P=tuneget V=1/1 B=0 scale=0.70 512x512 PNG]
filesizedescription
Tune-51939-cont.abc 141 ABC music file with the extracted tune(s)
Tune-51939-cont.ps 6 PostScript
Tune-51939-cont.txt 141 Plain-text file with the extracted tune(s)
Tune-51939-dance.abc 142 ABC music file with the extracted tune(s)
Tune-51939-dance.ps 6 PostScript
Tune-51939-dance.txt 142 Plain-text file with the extracted tune(s)
Tune-51939-get.log 7835 Log file, useful mostly for debugging
These files should be available for 24 hours.