Unresolved Linker error ------I am desperate ------

I have imported a type_library from a DLL. Cdo.dll and was apply to use the
.CPP in the application, and all went well.

I have added the object created from the application into a DLL application
and the head break loose. I am getting "Unresolved linker" error in the type
library. I decided to take the OBJ out, and instead, added the type library
".CPP" file, and the same error has continued. This works very well in the
application, but not in the DLL. This is the code that produces this error

CDOObject::CDOObject(const char* name, const char* password)
{
    newSession = 0;

::CoCreateInstance(CLSID_Session,0,CLSCTX_REMOTE_SERVER,DIID__Session,(LPVOI
D*)&newSession);
    curSession = newSession;
    curSession.set_Session_(WideString("MAPI.SESSION"));
    curSession.Logon(name,password);
    cdoObj = this;

Quote
}

The error get created  right at the CoCreateInstance.

Please, I am desperate. I have had the confidence that since it work with
the application, It will work with DLL.

I need help please.