UPDATE:
I did the Save As method as have the file setup fine now.
I think I've identified the cause of the Opening old file message. I copied and pasted a spread layout into a new document, so i could give it to someone else to work on. In this new document, I selected all and copied. I got the same deal as before, where it kept telling me it was opening the old document, except this time it was saying it was opening the 2010 file, not the 2009.
So, seeing as how this was just a single spread, I was able to keep selecting more and more objects and copy them until the message appeared again.
The cause, it seems, is a cross-reference I have set up in one of the text boxes. I use these throughout the catalog, to reference products on other pages. (ex: See our complete line of bags on page 32.) I set these up last year so that this year, when I shuffle pages, all the references will update themselves.
Even though it says its it's opening the document, it never does though…. Unless, you go to the Cross Reference panel and try to edit it. At that point, InD does open the referenced file.
Glad I figured that out. I don't think I set up the cross references wrong. I guess this is just one of those things that'll just have to happen.