COM

//Use GIT to store IWebLog marshalled interface so can call, unmarshall and use from write thread
g_pGIT = 0;
ATLTRACE("Messemger: Calling CoCreateInstance on CLSID_StdGlobalInterfaceTable\n");
hr = ::CoCreateInstance(CLSID_StdGlobalInterfaceTable,NULL,CLSCTX_INPROC_SERVER,IID_IGlobalInterfaceTable, reinterpret_cast<void **>(&g_pGIT));
if(FAILED(hr))
{	
	nErrID = IDS_CREATE_GIT_FAILED; 
	__leave;
}

// Registers a specified interface on an object residing in one apartment of a process as a global 
// (process-wide) interface, allowing other apartments access to that interface.
hr = g_pGIT->RegisterInterfaceInGlobal(m_pIWebLog,IID_IWebLog, &g_dwCookie);
if(FAILED(hr))
{
	nErrID = IDS_REG_OBJ_IN_GIT; 
	__leave;
}

1. all threads that create COM servers are pumping messages, i.e. they are UI threads
2. every thread that do any kind of COM stuff initializes the COM library with a call to ::CoInitialize() or one of its equivalents
3. your proxy-stub is properly registered, or your typelib is properly registered if your doing typelib marshalling

*      DECLARE_INTERFACE(iface) is used to declare an interface that does
*      not derive from a base interface.
*      DECLARE_INTERFACE_(iface, baseiface) is used to declare an interface
*      that does derive from a base interface.