Change public Guid pIID to IntPtr and marshal your guid directly to an allocated memory block and this struct will work with CoCreateInstanceEx.
An IntPtr is a pointer to a memory location (unmanaged) that adapts to the platform it is running on (64-bit, etc.) UNLIKE a standard int/Integer. You should always use this type for unmanaged calls that require it, even though an int will appear to work on your development machine.
