Recentf mode doesn't work

[LaserDoodads Info]

The fastest way to see the problem is like this.

Emacs -Q 
M-x recentf-mode
C-x C-f _emacs
M-x recentf-save-list

At this point a window pops up named *Warnings*.  The sole contents of the 
buffer is:

Warning (emacs): recentf mode: Wrong type argument: stringp, nil

Turning debug-on-error does not result in debug being entered.
This problem must be fairly recent since I use recentf daily and recompile from 
CVS weekly.



In GNU Emacs 22.0.50.1 (i386-msvc-nt5.1.2600)
of 2005-07-09 on LD1
X server distributor `Microsoft Corp.', version 5.1.2600
configured using `configure --with-msvc (12.00)'

Important settings:
 value of $LC_ALL: nil
 value of $LC_COLLATE: nil
 value of $LC_CTYPE: nil
 value of $LC_MESSAGES: nil
 value of $LC_MONETARY: nil
 value of $LC_NUMERIC: nil
 value of $LC_TIME: nil
 value of $LANG: ENU
 locale-coding-system: cp1252
 default-enable-multibyte-characters: t