ws_elk fails to build under windows

21> Creating library C:/build17/bin/Debug/ws_elk.lib and object C:/build17/bin/Debug/ws_elk.exp
21>WsELKPlugin.obj : error LNK2001: unresolved external symbol "public: virtual class CEspApplicationPort * __thiscall CEspProtocol::queryApplicationPort(int)" (?queryApplicationPort@CEspProtocol@@UAEPAVCEspApplicationPort@@H@Z)
21>WsELKPlugin.obj : error LNK2001: unresolved external symbol "public: virtual void __thiscall CEspProtocol::initPersistentHandler(struct IPropertyTree *)" (?initPersistentHandler@CEspProtocol@@UAEXPAUIPropertyTree@@@Z)
21>WsELKPlugin.obj : error LNK2001: unresolved external symbol "public: virtual void __thiscall CEspProtocol::addPersistent(class ISocket *)" (?addPersistent@CEspProtocol@@UAEXPAVISocket@@@Z)