How to call unmanaged c++ dll in wcf library?

I want to call c++ method from wcf service for get ip camera status.

Bellow code run successfully using wpf application but i want to run this method in wcf library then consume in wpf application.

when call method from wcf library then throw exeption. "An attempt was made to load a program with an incorrect format. (Exception from HRESULT: 0x8007000B)"

Hide Copy Code

[DllImport("dhnetsdk.dll")]

private static extern bool CLIENT_CapturePicture(int hPlayHandle, string pchPicFileName);

Please give solution on urgent basis.

Thanks & Regards

Chandrashekhar Sharma