[Exim] Multiple smtp auth methods

I am trying to configure smtp auth on a mailserver where both local user
and virtual users can login, I have lookups that work on their own so I
know my auth systems are working fine.
So to combine the I am trying to use the conditional expansion, in this
case an 'or'. The auth driver is below along with a login attempt that
isn't in the local passwd file and so the pam lookup fails but the
second condition should force it to succeed.
The relevent out put from "exim -bh 193.1.219.148 -d auth" is below.

I know i am missing something but what is it.

plain_login:
  driver = plaintext
  public_name = PLAIN
  server_prompts = :
  server_condition = ${if or \
        {\
          { pam{$2:$3} } \
          { true } \
        }\
        {yes}{no} \
      }

auth plain AGN3aGl0dGFrQHNhZ2UtaWUub3JnAHNlY3JldA==
SMTP<< auth plain AGN3aGl0dGFrQHNhZ2UtaWUub3JnAHNlY3JldA==
host in smtp_accept_max_nonmail_hosts? yes (matched "*")
Running PAM authentication for user "cwhittak@???"
PAM error: Authentication service cannot retrieve authentication info.
plain_login authenticator:
$1 =
$2 = cwhittak@???
$3 = secret
expansion failed: Authentication service cannot retrieve authentication info.
SMTP>> 435 Unable to authenticate at present
435 Unable to authenticate at present
LOG: MAIN REJECT
plain_login authenticator failed for grainne.heanet.ie (sdfsd) [193.1.219.148]: 435 Unable to authenticate at present: Authentication service cannot retrieve authentication info.

--
Colin Whittaker    colin.whittaker@???    Mob: +353 86 8211965
HEAnet NOC         noc@???                Tel: +353 1 6609040