A call comes in. If it is to a VOIP user, it will be routed to kamailio, and eventually go to the ldap lookup route: route[10] to look up the user.
This is always successful (LDAP can connect).
It will then look up user preferences (call forwarding etc.) from SQL in route[12] and route based on this result in route[13].
If the result is "CFU (call forward unconditional) = on", the URI is changed and route[10] (LDAP lookup) is called again.
This is always successful (LDAP can connect).
If the result is "CFB (call forward busy) = on" and the user is busy, the URI is changed and route[10] (LDAP lookup) is called again.
This is also always successful (LDAP can connect).
If the result is "CFNR (call forward no reply) = on", the timeout is changed and the call is delivered to the phone through route[14] (location) and route[15] (relay).
If the user does not answer, the URI is changed in failure_route[1] and route[10] is called.
For some unknown reason, ldap_search always fails in this scenario with the messages: "ldap_session not found", "couldn't get ldap session" and then "no LDAP entry found".
Why?
And why does this result in the -1 return code and not the -2 return code for ldap_search?

Dec 27 13:31:55 [3373]: INVITE received from sip:<CALLER>@<SBC_IP> <source IP: <SBC_IP>> to sip:<CALLEE>@<KAM_IP>:
Dec 27 13:31:55 [3373]: ERROR:ldap:ldap_reconnect: [ldapprod]: LDAP reconnect successful
Dec 27 13:31:55 [3373]: ROUTE 10: LDAP returned: UID = <UID>, voipSipPrimaryUri = <PRIMARY_URI>, voipExtensionUri = sip:<CALLEE>@<DOMAIN>
Dec 27 13:31:55 [3373]: ROUTE 12: Effective user properties for UID <UID>: CFU: off <FORWARDTO>, CFB: off <FORWARDTO>, CFNR: on:25 <FORWARDTO>, CFNC: off <FORWARDTO>, VM: <CALLEE>, busy_level: 1, DBrows: 1
Dec 27 13:31:55 [3373]: -------------------- Calling sip:<CALLEE>@<DOMAIN> for 25 seconds. --------------------
Dec 27 13:31:55 [3373]: ROUTE 15: Sending 105 INVITE from sip:<CALLER>@<SBC_IP> to sip:<CALLEE>@<CALLEE_IP> (via <<null>>)
Dec 27 13:31:55 [3383]: Response 100 Trying to Cseq 102 INVITE received from <PROTO>:<CALLEE_IP>:<PORT>
Dec 27 13:31:55 [3385]: Response 180 Ringing to Cseq 102 INVITE received from <PROTO>:<CALLEE_IP>:<PORT>

Dec 27 13:32:20 [3388]: FAILURE_ROUTE 1: Timeout for: 104 INVITE from <CALLER> -> <CALLEE>
Dec 27 13:32:20 [3388]: -------------------- Forwarding on no reply to <FORWARDTO> --------------------
Dec 27 13:32:20 [3388]: ERROR:ldap:get_connected_ldap_session: [ldapprod]: ldap_session not found
Dec 27 13:32:20 [3388]: ERROR:ldap:lds_search: [ldapprod]: couldn't get ldap session
Dec 27 13:32:20 [3388]: INFO:ldap:ldap_search_impl: no LDAP entry found
Dec 27 13:32:20 [3388]: ROUTE 11: Number lookup results for <FORWARDTO>: Node: VOIP.
Dec 27 13:32:20 [3388]: CONFIG ERROR: VOIP number not found in LDAP. Hanging up.
Dec 27 13:32:20 [3373]: Response 487 Request Cancelled to Cseq 102 INVITE received from <PROTO>:<CALLEE_IP>:<PORT>

# LDAP lookup for UID and primary URI
route[10] {
...
  ldap_search("ldap://ldapprod/<DN>?uid,voipSipPrimaryUri,voipExtensionUri?one?(&(objectClass=voipAddress)(|(voipSipUri=sip:$rU@uio.no)(|(voipSipUri=$var(uri))(voipSipUri=$var(e164uri)))))");
  if ($retcode < 1) {
   switch ($retcode) {
   case -1:
    # no LDAP entry found
    route(11);
    return(1);
   case -2:
    # internal error
    sl_send_reply("500", "Internal server error");
    exit;
   }
  }
  ldap_result("uid/$avp(s:uid)");
  $avp(s:exten) = null;
  if (!ldap_result("voipExtensionUri/$avp(s:exten)")) {
   xlog("L_INFO", "voipExtensionUri not found.\n");
  }
  if (!ldap_result("voipSipPrimaryUri/$avp(s:p-uri)")) {
   xlog("L_WARN", "voipSipPrimaryUri not found.\n");
   #exit here?
  }
  if (isflagset(1)) {
   xlog("L_INFO", "ROUTE 10: LDAP returned: UID = $avp(s:uid), voipSipPrimaryUri = $avp(s:p-uri), voipExtensionUri = $avp(s:exten)\n");
  }
  if $avp(s:exten) != null {
   $ru=$avp(s:exten);
  } else {
   $ru=$avp(s:p-uri);
  }
  route(12);
}
}

# Call forwarding logic
route[13] {
if (is_method("INVITE")) {
  $avp(s:uio_timer_avp) = "300";
  if ($avp(s:cfu_status) == "on") {
   # Forward immediately
   xlog("L_INFO", "-------------------- $rU forwarded unconditionally to $avp(s:cfu_number). --------------------\n");
   $rU = $avp(s:cfu_number);
   route(10);
  }
...
   if ( $var(dlg_busy) >= $avp(s:busy_level) ) {
    if ($avp(s:cfb_status) == "on") {
     xlog("L_INFO", "-------------------- $rU has $var(dlg_busy) active calls. Treshold $avp(s:busy_level). Forwarding on busy to $avp(s:cfb_number) --------------------\n");
     $rU = $avp(s:cfb_number);
     route(10);
    }
...
   else if ($avp(s:cfnr_status) == "on") {
    # Forward to phone with timeout then to $avp(s:cfnr_number).
    # t_set_fr($avp(s:cfnr_timeout) + "000"); # Recommended method in 3.1. Function does not exist in 1.5. Using old method (avp).
    $avp(s:uio_timer_avp) = $avp(s:cfnr_timeout);
    xlog("L_INFO", "-------------------- Calling $ru for $avp(s:uio_timer_avp) seconds. --------------------\n");
    route(14);
   }
...
}

failure_route[1] {
...
  if $avp(s:cfnr_status) == "on" {
   if (isflagset(1)) {
    xlog("L_INFO", "FAILURE_ROUTE 1: Timeout for: $mi $rm from $fU -> $rU\n");
   }
   revert_uri();
   $rU = $avp(s:cfnr_number);
   xlog("L_INFO", "-------------------- Forwarding on no reply to $rU --------------------\n");
   route(10);
  }
...
}