Thanks. I did create it by archiving the messages, rather than by just renaming the Outlook.pst file, and I renamed it inside Outlook to Archive 2012 as well, so it's peculiar that it wouldn't index.
I seem to have worked around the problem by clearing the index, indexing only the Archive 2012 file, and then selecting all the other files and archinving them as well. I checked by deleting a message from the Archive 2012 file, and after X1 re-indexed, that message was gone from the index, so it appears all is now well. If it happens again, I'll just try removing and re-adding the profile, as that's obviously an easier solution.
I seem to have worked around the problem by clearing the index, indexing only the Archive 2012 file, and then selecting all the other files and archinving them as well. I checked by deleting a message from the Archive 2012 file, and after X1 re-indexed, that message was gone from the index, so it appears all is now well. If it happens again, I'll just try removing and re-adding the profile, as that's obviously an easier solution.