I concur with CPL Nelson, sounds like an incomplete or corrupt archive. Have you tried re-downloading?
... you can always first run Command->Test Archive from winRAR (if that's what you are using) to check your archive(s) first. If you get the same error (which I suspect you will) you will have to re-download. Admittedly, it is odd you would have the problem with both files, that is, unless you were downloading them both at the same time.
