Got HTTP status 404 Not Found for "http://john-chambers.us/~jc/music/book/cache/Tune-20857-hornpipe.abc/tmp"
pngcmd="(./ps2png 512 512 /Users/jc/w/tmp/Tune-3074-tmp.ps) >>/Users/jc/w/tmp/Tune-3074-get.log 2>&1" returned status 256
http://john-chambers.us/~jc/music/book/cache/Tune-20857-hornpipe.abc/tmp

Error exit status 256; here are some files to check:
[get.cgi V=1/1 B=0 scale=0.55 512x512 PNG]
filesizedescription
Coll_30741.log 283409 Log file, useful mostly for debugging
Coll_30743.log 468210 Log file, useful mostly for debugging
Coll_30746.log 263810 Log file, useful mostly for debugging
Form_3074.log 906 Log file, useful mostly for debugging
Tune-3074-get.log 3997 Log file, useful mostly for debugging
Tune-3074-tmp.abc 161 ABC music file with the extracted tune(s)
Tune-3074-tmp.ps 6 PostScript
Tune-3074-tmp.txt 161 Plain-text file with the extracted tune(s)
Tune-30741-get.log 6491 Log file, useful mostly for debugging
Tune-30742-get.log 181138 Log file, useful mostly for debugging
Tune-30743-get.log 2874 Log file, useful mostly for debugging
Tune-30745-get.log 4839 Log file, useful mostly for debugging
Tune-30747-get.log 7997 Log file, useful mostly for debugging
Tune-30749-get.log 8326 Log file, useful mostly for debugging
These files should be available for 24 hours.