make doc error on current master

Hi folks

I haven't build lilypond for a long time. Can you please remind me how 
to debug and solve this error?

$ make LANGS='en' doc
Making input/regression/out-www/collated-files.texi < tely
Command '/home/fede/src/lilypond/build/out/bin/lilypond \
               -I /home/fede/src/lilypond/input/regression \
                        -dseparate-page-formats=ps,pdf 
-dinclude-eps-fonts -dgs-load-fonts --header=doctitle 
--header=doctitleen --header=texidoc --header=texidocen 
-dcheck-internal-types -danti-alias-factor=2 
-dfont-ps-resdir=/home/fede/src/lilypond/build/out-fonts -O TeX-GS -I 
"/home/fede/src/lilypond/input/regression" -I "." -I 
"/home/fede/src/lilypond/build/input/regression" -daux-files 
-dread-file-list -dno-strip-output-dir -dtall-page-formats=eps,png 
"/home/fede/src/lilypond/build/out/lybook-db/snippet-names-9f571599ce826614c623dd2bc0ba6fe9.ly"' 
returned non-zero exit status 1.
make[3]: *** [/home/fede/src/lilypond/build/.././make/ly-rules.make:39: 
out-www/collated-files.texi] Error 1
make[2]: *** 
[/home/fede/src/lilypond/build/.././make/generic-targets.make:138: WWW] 
Error 2
make[1]: *** 
[/home/fede/src/lilypond/build/.././make/generic-targets.make:138: WWW] 
Error 2
make: *** 
[/home/fede/src/lilypond/build/.././make/generic-targets.make:143: doc] 
Error 2

snippet-names-9f571599ce826614c623dd2bc0ba6fe9.ly contains a long list 
of file names. Which one is causing the failure?