Got HTTP status 404 Not Found for "http://john-chambers.us/~jc/music/book/cache/Tune-8866-slipjig.abc/tmp"
pngcmd="(./ps2png 512 512 /Users/jc/w/tmp/Tune-5578-tmp.ps) >>/Users/jc/w/tmp/Tune-5578-get.log 2>&1" returned status 256
http://john-chambers.us/~jc/music/book/cache/Tune-8866-slipjig.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_5578.log 259610 Log file, useful mostly for debugging
Coll_55781.log 743219 Log file, useful mostly for debugging
Coll_55785.log 268010 Log file, useful mostly for debugging
Form_55782.log 827 Log file, useful mostly for debugging
Form_55785.log 863 Log file, useful mostly for debugging
Tune-5578-get.log 3987 Log file, useful mostly for debugging
Tune-5578-tmp.abc 159 ABC music file with the extracted tune(s)
Tune-5578-tmp.ps 6 PostScript
Tune-5578-tmp.txt 159 Plain-text file with the extracted tune(s)
Tune-55783-get.log 7142 Log file, useful mostly for debugging
Tune-55784-get.log 12199 Log file, useful mostly for debugging
Tune-55785-get.log 9499 Log file, useful mostly for debugging
Tune-55787-get.log 14524 Log file, useful mostly for debugging
Tune-55788-get.log 177862 Log file, useful mostly for debugging
Tune-55789-get.log 6207 Log file, useful mostly for debugging
These files should be available for 24 hours.