pscmd="(jcabc2ps /Users/jc/w/tmp/Tune-84207-Gow4.abc -F fmt/pdf_70.fmt +s 0.70 +maxs 2000 )>/Users/jc/w/tmp/Tune-84207-Gow4.ps 2>>/Users/jc/w/tmp/Tune-84207-get.log" returned status 35584.
pngcmd="(./ps2png 512 512 /Users/jc/w/tmp/Tune-84207-Gow4.ps) >>/Users/jc/w/tmp/Tune-84207-get.log 2>&1" returned status 256
http://john-chambers.us/~jc/music/book/Gow/Gow4/Gow4.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-84207-Gow4.abc 2132 ABC music file with the extracted tune(s)
Tune-84207-Gow4.ps 38391 PostScript
Tune-84207-Gow4.txt 2132 Plain-text file with the extracted tune(s)
Tune-84207-get.log 5629 Log file, useful mostly for debugging
These files should be available for 24 hours.