Can't create instance of AcadApplication from C#.

Hello Everyone,

I am new to programming AutoCad using .Net. I am trying to create a standalone C#/.Net Application to manipulate the dwg files.

While creating an instance of AcadApplication using following code, I am getting a crash which I can't comprehend completely.

Type acType = Type.GetTypeFromProgID("AutoCAD.Application.18.1");
AcadApplication acApp = null;
acApp = (AcadApplication)Activator.CreateInstance(acType,true);

 I get the followng error message.

Unable to cast COM object of type 'Autodesk.AutoCAD.Interop.AcadApplicationMinorVersion1Class' to interface type 'AutoCAD.AcadApplication'. This operation failed because the QueryInterface call on the COM component for the interface with IID '{070AA05D-DFC1-4E64-8379-432269B48B07}' failed due to the following error: No such interface supported (Exception from HRESULT: 0x80004002 (E_NOINTERFACE)).

Although, I can see an instance of acad.exe getting started in taskmanager, but value of acApp is still null.

Other informations:

Visual Studio Version : VS 2012 Express Edition

AutoCaD Version : AutoCAD 2012 x64 version

OS : Windows 7, x64 version.

Thanks in advance,

Durgesh