I want to use a c + + DLL

I want to use a c + + DLL, the DLL in the Assets/Plugins/directory, and can work properly in my PC, but does suggest the mistakes in my colleague's PC Failed to load 'Assets/Plugins/cai-nav-rcn.dll' with error '操作成功完成。 ', GetDllDirectory returned ''. If GetDllDirectory returned non empty path, check that you're using SetDirectoryDll correctly. I tested 4 PCS, use unity3d 5.2.3 requires Windows 64 OS, two of the PC can work properly, not two I need help