problem with ckpasswd..

I've got a server with some local group
fully accessible by ckpasswd authentication.
What I want is to put some user-id that
could only read some group.

my previous readers.conf was

auth "regular users" {
   auth: "ckpasswd -d /usr/local/news/db/regularusers"
}
access "regular users" {
 users: "*"
newsgroup: "*,!junk,!control,!control.*"
access "Read Post"
}

and it worked with my perl scripts.
i've tried to just add another auth
that match another file.
something like

auth "read only users" {
     auth: "ckpasswd -d /usr/local/news/db/readonly"
}

access "read only users" {
 users: "*"
newsgroup: "*,!this,!that!"
access "Read"
}

but then i've got some ckpasswd error with the previous (regular) users.

what's the error?
how could i do this thing?
luca