[exim] Message in the panic.log: unknown named domain list "…

Hi List

I've recently noticed the following messages cropping up in my exim
panic.log

unknown named domain list "+whitelist_senders"

I've no idea, based on a look at my configuration, why this should be the
case, and woulod appreciate it if anyone on thhe list could point out
what's wrong with this whitelisting configuration? My whitelisting
configuration for whitelisting senders from RBL filtering and spam
filtering is as follows:

---

addresslist whitelist_sender_domains =
wildlsearch;/etc/exim/whitelist_sender
addresslist whitelist_senders = wildlsearch;/etc/exim/whitelisted_addresses

.
.
.

  accept
    senders     = +whitelist_sender_domains : +whitelist_senders : *@
qtndealers.co.za : 082fax2email@??? : faxemail@??? :
tikizani@??? :\
                   cornish05@??? : greggandem@??? :
rogerh@??? :\
                   *@co.za

.
.
.

  # reject spam at high scores (> 7)
  deny   message   = This message scored $spam_score spam points.
         condition = ${if <{$message_size}{20k}{1}{0}}
         spam      = nobody:true
         !hosts    = +ok_hosts
         !sender_domains  = +whitelist_senders
         condition = ${if >{$spam_score_int}{63}{1}{0}}
---

Many Thanks in advance!
Traiano