Got HTTP status 404 Not Found for "http://john-chambers.us/~jc/music/book/JamesOswald/CPC/20571_Love_Slip.abc/all"
pngcmd="(./ps2png 512 512 /Users/jc/w/tmp/Tune-13958-all.ps) >>/Users/jc/w/tmp/Tune-13958-get.log 2>&1" returned status 256
http://john-chambers.us/~jc/music/book/JamesOswald/CPC/20571_Love_Slip.abc/all

Error exit status 256; here are some files to check:
[get.cgi V=1/1 B=0 scale=0.55 512x512 PNG]
filesizedescription
Tune-13958-all.abc 167 ABC music file with the extracted tune(s)
Tune-13958-all.ps 6 PostScript
Tune-13958-all.txt 167 Plain-text file with the extracted tune(s)
Tune-13958-get.log 13360 Log file, useful mostly for debugging
These files should be available for 24 hours.