expire-alist syntax

[Matt Price <matt.price@utoronto.ca>]

hi folks,

trying to set up auto-expiry but running into an error with
expire-alist:
Wrong type argument: numberp, nil
with wl-expire-alist set thus:

(setq wl-expire-alist 
 '(("^\\%inbox$" (date 40) ".archive")	
  ("/(flag:digest)/%inbox:pricemat/clear@mailbox126.utcc.utoronto.ca:993" (date 40) ".archive")
))

--- 
the second entry is there just bc i don't understand emacs regexes
every well & mostly work with the filter folder explicitly named in
that line.  anyway the format there looks about like this example
from the manual:
("^\\+outbox$"  (number 300) "$outbox;lha")

if anyone can see what the problem is i'd be absolutely grateful!
thanks,

matt