diff -urN netxms-1.2.17/src/server/core/node.cpp netxms-1.2.17.new/src/server/core/node.cpp
--- netxms-1.2.17/src/server/core/node.cpp	2014-10-18 22:36:00.000000000 +0300
+++ netxms-1.2.17.new/src/server/core/node.cpp	2014-10-27 21:13:55.000000000 +0200
@@ -5326,6 +5326,13 @@
          else if (iface->getPeerNodeId() != 0)
          {
             Node *peerNode = (Node *)FindObjectById(iface->getPeerNodeId(), OBJECT_NODE);
+            if (peerNode == NULL)
+            {
+               DbgPrintf(6, _T("Node::topologyPoll(%s [%d]): peer node set but node object does not exist"), m_name, m_id);
+               iface->clearPeer();
+               continue;
+            }
+
             if (peerNode->isDown())
                continue; // Don't change information about down peers
 
diff -urN netxms-1.2.17/src/server/include/nms_objects.h netxms-1.2.17.new/src/server/include/nms_objects.h
--- netxms-1.2.17/src/server/include/nms_objects.h	2014-10-18 22:36:00.000000000 +0300
+++ netxms-1.2.17.new/src/server/include/nms_objects.h	2014-10-27 21:15:56.000000000 +0200
@@ -692,7 +692,7 @@
 	void setPhysicalPortFlag(bool isPhysical) { if (isPhysical) m_flags |= IF_PHYSICAL_PORT; else m_flags &= ~IF_PHYSICAL_PORT; Modify(); }
 	void setManualCreationFlag(bool isManual) { if (isManual) m_flags |= IF_CREATED_MANUALLY; else m_flags &= ~IF_CREATED_MANUALLY; Modify(); }
 	void setPeer(Node *node, Interface *iface, LinkLayerProtocol protocol, bool reflection);
-   void clearPeer() { m_peerNodeId = 0; m_peerInterfaceId = 0; m_peerDiscoveryProtocol = LL_PROTO_UNKNOWN; Modify(); }
+   void clearPeer() { LockData(); m_peerNodeId = 0; m_peerInterfaceId = 0; m_peerDiscoveryProtocol = LL_PROTO_UNKNOWN; Modify(); UnlockData(); }
    void setDescription(const TCHAR *descr) { LockData(); nx_strncpy(m_description, descr, MAX_DB_STRING); Modify(); UnlockData(); }
 
 	void updateZoneId();