In grml 2014.11 full version both i386 and amd64, grml-lock fails giving the error
vlock: loading plugin "new" failed: No such file or directory

This is apparently because currently vlock's --new option is disabled in Debian
upstream due to a bug that was "too hard to fix":
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=702705
See this thread for details:
http://comments.gmane.org/gmane.linux.distributions.grml.devel/154

Not sure if grml wants to work on this, but it appears that Debian currently has
no plans of re-enabling the --new option.  Thus presumably unless something
changes, grml-lock will remain unable to lock X sessions indefinitely.  At least
that's what I think I gather.