reading the cache directly, can i just nnspool it?

[Greg Stark <gsstark@MIT.EDU>]

I've been using the cache a bit, and sometimes i want to browse all the saved
articles from some particular set of groups.  In particular I want to browse
all the saved articles from ephemeral nndoc digest groups made from browsing
comp.risks.  The cached articles from those digest groups aren't reachable any
other way, but it would be sort of nice to make an nnvirtual group that would
suck them all out of the cache into one group.

So i tried this:

(nnspool "cache"
         (nnspool-spool-directory "/mit/gsstark/News/cache")
         (nnspool-nov-directory "/mit/gsstark/News/cache")
         (nnspool-lib-dir "/mit/gsstark/News/cache")
         (nnspool-active-file "/mit/gsstark/News/active"))

I get this:
Couldn't request list: Opened server cache using directory /mit/gsstark/News/cache

This isn't really the most useful error message, 
nnspool-request-list isn't setting the status message, 
so the most recent status message is from the open request.
But, looking at the source this comes from trying to open the active file.

Where am i supposed to get an active file? 
Should  i be using a different backend?

greg