Stuart Henderson <stu@spacehopper.org> writes:

> I believe it should be setgid auth (mode 2755 or 2555).

I have the same error message with the following settings:

$ ls -l /tmp/xscreensaver/bin/xscreensaver
-r-xr-sr-x  1 root  auth  150616 Jul  8 11:16 /tmp/xscreensaver/bin/xscreensaver*
$ ls -l /tmp/xscreensaver/libexec/xscreensaver/xscreensaver-auth 
-r-xr-sr-x  1 root  auth  522400 Jul  8 11:16 /tmp/xscreensaver/libexec/xscreensaver/xscreensaver-auth*
-- 
Manuel Giraud