Got HTTP status 404 Not Found for "http://john-chambers.us/~jc/music/book/DftY/Preston.abc/1798"
pngcmd="(./ps2png 512 512 /Users/jc/w/tmp/Tune-4099-1798.ps) >>/Users/jc/w/tmp/Tune-4099-get.log 2>&1" returned status 256
http://john-chambers.us/~jc/music/book/DftY/Preston.abc/1798

Error exit status 256; here are some files to check:
[get.cgi V=1/1 B=0 scale=0.55 512x512 PNG]
filesizedescription
Coll_4099.log 286209 Log file, useful mostly for debugging
Coll_40990.log 729220 Log file, useful mostly for debugging
Coll_40991.log 445808 Log file, useful mostly for debugging
Coll_40995.log 457009 Log file, useful mostly for debugging
Coll_40996.log 897222 Log file, useful mostly for debugging
Form_40992.log 978 Log file, useful mostly for debugging
Form_40998.log 990 Log file, useful mostly for debugging
Tune-4099-1798.abc 149 ABC music file with the extracted tune(s)
Tune-4099-1798.ps 6 PostScript
Tune-4099-1798.txt 149 Plain-text file with the extracted tune(s)
Tune-4099-get.log 3940 Log file, useful mostly for debugging
Tune-40995-get.log 1607 Log file, useful mostly for debugging
These files should be available for 24 hours.