无法解析的外部符号 咋回事儿呢?该咋办?

1>TryThirdDlg.obj : error LNK2019: 无法解析的外部符号 "public: int __cdecl ConnMgr::CreateConnection(void * *,struct _CONNMGR_DESTINATION_INFO *)" (?CreateConnection@ConnMgr@@QAAHPAPAXPAU_CONNMGR_DESTINATION_INFO@@@Z)，该符号在函数 "public: void __cdecl CTryThirdDlg::OnBnClickedDownload(void)" (?OnBnClickedDownload@CTryThirdDlg@@QAAXXZ) 中被引用 1>TryThirdDlg.obj : error LNK2019: 无法解析的外部符号&nb