Set access permission just to particular user

I have a shared folder in my local network. now i want to deny everyone to access to it and just allow to a part开发者_StackOverflow中文版icular user. I used DirectoryInfo and DirectorySecurity classes but i could only deny everyone and when that particular user wants to access to this folder recieve "Access to this path is denied" message. Please help me.

How to programmatically set NTFS file system folder permissions by using Active Directory Service Interfaces in Microsoft Visual C#