I had everything set correctly, too.  I have no idea what it was, but these are the steps I followed to fix it:

1. Completely Delete the subweb from IIS

2. Completely Delete the subweb's directory from disk

3. Create a directory for the subweb with a different name that you had before

4. Extract the archive into that directory

5. Re-establish your subweb under IIS

After that, everything worked just fine - I don't know if it's something that I neglected to copy over [?] or just a strange IIS issue.