pngcmd="(./ps2png 512 512 /Users/jc/w/tmp/Tune-20708-CR4-abc2.ps) >>/Users/jc/w/tmp/Tune-20708-get.log 2>&1" returned status 256
http://john-chambers.us/~jc/music/book/Gow/CR4-abc2.abc

Error exit status 256; here are some files to check:
[get.cgi V=1/1 B=0 scale=0.55 512x512 PNG]
filesizedescription
Tune-20708-CR4-abc2.abc 94295 ABC music file with the extracted tune(s)
Tune-20708-CR4-abc2.ps 937902 PostScript
Tune-20708-CR4-abc2.txt 94295 Plain-text file with the extracted tune(s)
Tune-20708-get.log 62599 Log file, useful mostly for debugging
These files should be available for 24 hours.