updating Assembly in GAC

Question

Hi
i have created a C# DLL in VS2003 and installed it in GAC with WISE installer which actually register the dll in gac and add registry key.
i am calling this dll following way in vbscript

set TestAddaptor = CreateObject("Gen.TestAdaptor")
set aList = TestAddaptor.GetList("Gen.myList")

TestAddaptor is a c++ assembly which call my dll like this

GetList(BSTR myListProgId)
{
  CComObject<XMLList>* pObj;
  hr = CComObject<XMLList>::CreateInstance(&pObj);
  if (FAILED(hr)){return hr; }
  hr = pObj->InternalInitialize(myListProgId);//error here
}
when i first time installed the dll and access it with above script it works fine
but when i change the version number after some updates in the code and install it again its not working
in event log its giving the error for Invalid class string.
i even remove the previous version before new installation and restart my pc and iisreset.
this happen for all the dlls i m working they all work first time same error after new version of dll

can you please help me i m stuck here.
thanks a lot