How to use custom dll in .net in classic ASP ?

I have written one class library using C#.NET. I am trying to use this library in my ASP page using following code :-

Set obj=Server.CreateObject("TestDll.SampleDll")

But I am getting following error
Server object error 'ASP 0177 : 800401f3'
Server.CreateObject Failed

I have local IIS 7 server with Win 7 as operating system. I have already tried following options :-
1. Registered this dll in GAC
2. Adding this dll in Registry using Regsvr (but not able to do that, getting error "The module dll was loaded but the entry-point DllRegisterServer was not found.Make sure that dll is a valid DLL or OCX file and then try again")
3. EXposed my class library to COM (using [assembly: ComVisible(true)]) in AssemblyInfo.cs

Can anybody let me know what am I missing here ? I need to use my custom dll in ASP application.

Quick suggestions will be really appreciable.

Regards                                                                                                                                                                                    Sarang Deshpande