I am not quite sure why we cannot load one assembly into a appDomain if the assembly is alreadly loaded in sharedomain, if the security resctriction in the two appDomain differs. If we do so, we will get the "security permission grant set is incompatible between appdomains" exception.

You may ask how to load a customer assembly into shared domain. One customer shows the way:

int _tmain(int argc, _TCHAR* argv[])
{

  HRESULT hr = S_OK;
  ICorRuntimeHost *pHost = NULL;
  _ObjectHandle *pObjHandle = NULL;
  IHost *pHostObjInPrimaryAppdomain = NULL;
  IHost *pPR = NULL;
  _AppDomain *pSecDomain = NULL;
  IUnknown     *pAppDomainUnkPrimary = NULL;
  _AppDomain *pPrimaryDomain = NULL;
  _ObjectHandle *pObjHandleInPrimaryAppdomain = NULL;
  _AppDomain *pSecDomainUnk = NULL;
  _Delegate *pDelegate = NULL;

  hr = CoInitialize(NULL);
  if (FAILED(hr))
  {
     return -1;
  }

  // Load the net framework
  hr = CorBindToRuntimeEx (
          NULL,//L"v1.1.4322",
          L"svr",
          STARTUP_LOADER_SAFEMODE | STARTUP_LOADER_OPTIMIZATION_MULTI_DOMAIN_HOST,
          CLSID_CorRuntimeHost,
          IID_ICorRuntimeHost,
          (LPVOID *)&pHost);

  if (FAILED(hr) || !pHost)
  {
     return -1;
  }
 
  hr = pHost->Start();
  if (FAILED(hr))
  {
     return -1;
  }

  hr = pHost->GetDefaultDomain(&pAppDomainUnkPrimary );
  if ((FAILED(hr))||(!(pAppDomainUnkPrimary)))
  {
    return -1;
  }

  hr = pAppDomainUnkPrimary->QueryInterface(__uuidof(_AppDomain),
                                        (void**) &pPrimaryDomain);
  pAppDomainUnkPrimary->Release();
  if (FAILED(hr) || !pPrimaryDomain)
  {
   
    return -1;
  } 

  hr = pPrimaryDomain->CreateInstance(
    _bstr_t("ManagedHost"),// assembly name
    _bstr_t("ManagedHost.Host"),// type name
    &pObjHandleInPrimaryAppdomain);// returned handle to object

Here, the ManagedHost is loaded into the SharedDomain, and the CreateInstance function call also creates a new domain, where the ManagedHost is loaded again.

However, in CLR2.0, with the same code, the ManagedHost will not be loaded into ShareadDomain anymore, thus I assume the exception can be avoided.

In fact, this topic is far away from the original quesiton the customer asked. The customer wants to challange the following MSDN statements marked red based on the test:

"When you use a Load method with a Byte[] parameter to load a common object file format (COFF) image, evidence is combined. Zone, Url and Site are inherited from the calling assembly, and Hash and StrongName are taken from the COFF assembly."

http://spaces.msn.com/eparg/blog/cns!59BFC22C0E7E1A76!525.entry