Got HTTP status 404 Not Found for "http://john-chambers.us/~jc/music/book/1798/Kerr_MM4-V2.abc"
pngcmd="(./ps2png 512 512 /Users/jc/w/tmp/Tune-16608-Kerr_MM4-V2.ps) >>/Users/jc/w/tmp/Tune-16608-get.log 2>&1" returned status 256
http://john-chambers.us/~jc/music/book/1798/Kerr_MM4-V2.abc

Error exit status 256; here are some files to check:
[P=tuneget V=1/1 B=0 scale=0.70 512x512 PNG]
filesizedescription
Tune-16608-24CountryDances_1808_Goulding_PD.abc 169 ABC music file with the extracted tune(s)
Tune-16608-24CountryDances_1808_Goulding_PD.ps 6 PostScript
Tune-16608-24CountryDances_1808_Goulding_PD.txt 169 Plain-text file with the extracted tune(s)
Tune-16608-Kerr_MM4-V2.abc 148 ABC music file with the extracted tune(s)
Tune-16608-Kerr_MM4-V2.ps 6 PostScript
Tune-16608-Kerr_MM4-V2.txt 148 Plain-text file with the extracted tune(s)
Tune-16608-get.log 8555 Log file, useful mostly for debugging
These files should be available for 24 hours.