Got HTTP status 404 Not Found for "http://john-chambers.us/~jc/music/book/cache/Tune-20371-hornpipe.abc/tmp"
pngcmd="(./ps2png 512 512 /Users/jc/w/tmp/Tune-8710-tmp.ps) >>/Users/jc/w/tmp/Tune-8710-get.log 2>&1" returned status 256
http://john-chambers.us/~jc/music/book/cache/Tune-20371-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_87107.log 466810 Log file, useful mostly for debugging
Form_8710.log 1769 Log file, useful mostly for debugging
Form_87102.log 1832 Log file, useful mostly for debugging
List87108.log 142 Log file, useful mostly for debugging
Tune-8710-get.log 4001 Log file, useful mostly for debugging
Tune-8710-tmp.abc 161 ABC music file with the extracted tune(s)
Tune-8710-tmp.ps 6 PostScript
Tune-8710-tmp.txt 161 Plain-text file with the extracted tune(s)
Tune-87100-get.log 6020 Log file, useful mostly for debugging
Tune-87103-get.log 0 Log file, useful mostly for debugging
Tune-87104-get.log 4346 Log file, useful mostly for debugging
Tune-87105-get.log 5824 Log file, useful mostly for debugging
Tune-87106-get.log 8099 Log file, useful mostly for debugging
Tune-87107-get.log 9607 Log file, useful mostly for debugging
Tune-87108-get.log 9000 Log file, useful mostly for debugging
Tune-87109-get.log 3949 Log file, useful mostly for debugging
These files should be available for 24 hours.