[exim] unknown ACL verb

Hi

I've been using the examples in the documention for exim 4.4* to setup
smtp-auth with cram-md5.
My setting in exim.conf are:

begin authenticators:

fixed_cram:
    driver = cram_md5
    public_name = CRAM-MD5
    server_secret = ${if eq{$1}{username}{password}deny}
    server_set_id = $1

Every time I try to authenticate though I get the following log event.
temporarily rejected AUTH CRAM-MD5: unknown ACL verb in "fixed_cram"

I also tried the PLAIN example but that gave me a similar message?

any ideas?

kind regards