Got HTTP status 404 Not Found for "http://john-chambers.us/~jc/music/session/Oivan_Ilo/Kipera-A-36-4.abc/polka"
pngcmd="(./ps2png 512 512 /Users/jc/w/tmp/Tune-4648-polka.ps) >>/Users/jc/w/tmp/Tune-4648-get.log 2>&1" returned status 256
http://john-chambers.us/~jc/music/session/Oivan_Ilo/Kipera-A-36-4.abc/polka

Error exit status 256; here are some files to check:
[get.cgi V=1/1 B=0 scale=0.55 512x512 PNG]
filesizedescription
Coll_46488.log 939219 Log file, useful mostly for debugging
Form_46482.log 965 Log file, useful mostly for debugging
Form_46489.log 1001 Log file, useful mostly for debugging
Tune-4648-get.log 4043 Log file, useful mostly for debugging
Tune-4648-polka.abc 164 ABC music file with the extracted tune(s)
Tune-4648-polka.ps 6 PostScript
Tune-4648-polka.txt 164 Plain-text file with the extracted tune(s)
These files should be available for 24 hours.