Excel addin

try changing your import to
 
#import "C:\Program Files\Microsoft Office\Office\EXCEL9.olb" \
            rename_namespace("Excel") rename("DialogBox","_DialogBox") rename("RGB","_RGB") \
            exclude("IFont","IPicture") raw_interfaces_only named_guids
 
I also prefer to put the app-specific import in the Addin.h to prevent name conflicts