pngcmd="(./ps2png 512 512 /Users/jc/w/tmp/Tune-21993-20671_.ps) >>/Users/jc/w/tmp/Tune-21993-get.log 2>&1" returned status 256
http://john-chambers.us/~jc/music/book/EliasHowe/MusiciansCompanionP2/20671_.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-21993-20671_.abc 33 ABC music file with the extracted tune(s)
Tune-21993-20671_.ps 6 PostScript
Tune-21993-20671_.txt 33 Plain-text file with the extracted tune(s)
Tune-21993-get.log 3994 Log file, useful mostly for debugging
These files should be available for 24 hours.