Got HTTP status 404 Not Found for "http://john-chambers.us/~jc/music/book/Tunes/CDfNH1783.abc"
pngcmd="(./ps2png 512 512 /Users/jc/w/tmp/Tune-6652-CDfNH1783.ps) >>/Users/jc/w/tmp/Tune-6652-get.log 2>&1" returned status 256
http://john-chambers.us/~jc/music/book/Tunes/CDfNH1783.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-6652-CDfNH1783.abc 147 ABC music file with the extracted tune(s)
Tune-6652-CDfNH1783.ps 6 PostScript
Tune-6652-CDfNH1783.txt 147 Plain-text file with the extracted tune(s)
Tune-6652-get.log 4053 Log file, useful mostly for debugging
Tune-66522-ViolaRuth_PWFT.abc 152 ABC music file with the extracted tune(s)
Tune-66522-ViolaRuth_PWFT.pdf 2217 Portable Data Format
Tune-66522-ViolaRuth_PWFT.ps 6 PostScript
Tune-66522-ViolaRuth_PWFT.txt 152 Plain-text file with the extracted tune(s)
Tune-66522-get.log 5006 Log file, useful mostly for debugging
These files should be available for 24 hours.