VBA for outlook  is not the same as for other apps because you have to do a lot
more set-up work.

Have you thought how you would identify the particular message  to deal with?
What if there were two relevant ones?

Would it be easier to use one of the (fairly cheap) outlook addins to extract
all attachments to a directory so you only had to find an excel  file in a
particular directory? IMO _anything_ is preferable to trying to get an
outlook macro to behave itself!