Got HTTP status 404 Not Found for "http://john-chambers.us/~jc/music/book/GM/Lockhings_Whim.abc/1753"
pngcmd="(./ps2png 512 512 /Users/jc/w/tmp/Tune-90133-1753.ps) >>/Users/jc/w/tmp/Tune-90133-get.log 2>&1" returned status 256
http://john-chambers.us/~jc/music/book/GM/Lockhings_Whim.abc/1753

Error exit status 256; here are some files to check:
[get.cgi V=1/1 B=0 scale=0.55 512x512 PNG]
filesizedescription
Coll_90133.log 438810 Log file, useful mostly for debugging
Form_90133.log 966 Log file, useful mostly for debugging
Tune-90133-1753.abc 154 ABC music file with the extracted tune(s)
Tune-90133-1753.ps 6 PostScript
Tune-90133-1753.txt 154 Plain-text file with the extracted tune(s)
Tune-90133-get.log 9585 Log file, useful mostly for debugging
These files should be available for 24 hours.