I want to achieve one thing. I want to use 32 bit COM type library from an Excel Add in. Note that 64-bit excel 2010 is installed on my machine. I have compiled the add in in 32 bits. But when i create instance of a COM class, it gives this error "retrieving the COM class factory for component with CLSID failed due to the following error Class not registered" Is it possible what I am trying to do ? Any suggestions (except using another version of Excel or 1 64 bit COM type library) ?