You should not return BSTR (or any "complex" type that various compilers compile in various ways). The recommended return type for COM methods is HRESULT (a 32-bit integer). Also, you must not release a BSTR you just allocated and return it to the caller.

Here is how you could layout your methods:

HRESULT STDMETHODCALLTYPE TVImpl::Login(BSTR PassWord, /*out*/ BSTR *pRead)
{
  ...
  *pRead = ::SysAllocString(L"blabla"); // allocate a BSTR
  ...
  // don't SysFreeString here, the caller should do it
  ...
  return S_OK;
}

If you were defining your interface in a .idl file, it would be something like:

interface IMyInterface : IUnknown
{
    ...
    HRESULT Login([in] BSTR PassWord, [out, retval] BSTR *pRead);
    ...
}

retval is used to indicate assignment semantics are possible for languages that support it, like what you were trying to achieve initially with code like this var read = obj.Login("mypass")