Got HTTP status 404 Not Found for "http://john-chambers.us/~jc/music/book/Kerr_MM/MMM2.abc"
pngcmd="(./ps2png 512 512 /Users/jc/w/tmp/Tune-8168-MMM2.ps) >>/Users/jc/w/tmp/Tune-8168-get.log 2>&1" returned status 256
http://john-chambers.us/~jc/music/book/Kerr_MM/MMM2.abc

Error exit status 256; here are some files to check:
[P=tuneget V=1/1 B=0 scale=0.70 512x512 PNG]
filesizedescription
Coll_81683.log 271685 Log file, useful mostly for debugging
Coll_81684.log 292760 Log file, useful mostly for debugging
Coll_81687.log 281520 Log file, useful mostly for debugging
Tune-8168-MMM2.abc 144 ABC music file with the extracted tune(s)
Tune-8168-MMM2.ps 6 PostScript
Tune-8168-MMM2.txt 144 Plain-text file with the extracted tune(s)
Tune-8168-get.log 3956 Log file, useful mostly for debugging
These files should be available for 24 hours.