Got HTTP status 404 Not Found for "http://john-chambers.us/~jc/music/book/DftY/Cahusac_24CD.abc/1758"
pngcmd="(./ps2png 512 512 /Users/jc/w/tmp/Tune-98353-1758.ps) >>/Users/jc/w/tmp/Tune-98353-get.log 2>&1" returned status 256
http://john-chambers.us/~jc/music/book/DftY/Cahusac_24CD.abc/1758

Error exit status 256; here are some files to check:
[get.cgi V=1/1 B=0 scale=0.55 512x512 PNG]
filesizedescription
Form_98353.log 866 Log file, useful mostly for debugging
Tune-98353-1758.abc 154 ABC music file with the extracted tune(s)
Tune-98353-1758.ps 6 PostScript
Tune-98353-1758.txt 154 Plain-text file with the extracted tune(s)
Tune-98353-get.log 3989 Log file, useful mostly for debugging
These files should be available for 24 hours.