[Exim] Dlopen failure, solaris 8 (sorry, redundant msg)

I'm using solaris 8 and want to auth users.

Running PAM authentication for user "imyaman"
PAM error: Dlopen failure
plain authenticator:
$1 =
$2 = imyaman
$3 = MYPASSWD
expansion failed: Dlopen failure
SMTP>> 435 Unable to authenticate at present: Dlopen failure
.
.
.
LOG: 0 MAIN REJECT
Authentication failed for (localhost.localhost) [210.220.144.136]: 435 Unable to authenticate at present: Dlopen failure

I added follwing lines to /etc/pam.conf

#>>>>
exim auth required /usr/lib/security/$ISA/pam_unix.so
exim auth required /usr/lib/security/$ISA/pam_permit.so
#>>>>

what is the problem?