In the public dial plan……
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 <extension name="mytest">
  <condition field="destination_number" expression="^(4412345678)$">
  <action application="set" data="domain_name=$${domain}"/>
   <action application="transfer" data="1000 XML default"/>
  </condition>
  </extension>

"1000" being a user under directory/default/
===========================================
<include>
  <user id="1000">
    <params>
     <param name="a1-hash" value="ffffffffffffffffffff"/>
      <param name="vm-disk-quota" value="1500"/>
       <param name="vm-a1-hash" value="ffffffffffffffffffff"/>
    </params>
    <variables>
      <variable name="toll_allow" value="uk_nopremium,int_standard,int_usaexpremium"/>
      <variable name="accountcode" value="1000"/>
      <variable name="user_context" value="default"/>
      <variable name="effective_caller_id_name" value="Some User"/>
    <variable name="effective_caller_id_number" value="00000000"/> -->
      <variable name="outbound_caller_id_name" value="$${outbound_caller_name}"/>
      <variable name="outbound_caller_id_number" value="$${outbound_caller_id}"/>
      <variable name="callgroup" value="mycallgroup"/>
    </variables>
  </user>
</include>

>You're getting it because it can't find the USER to call. How are you calling the users on this interface in your dialplan?