Files from Logic versions older than 5 need to first be opened in Logic 5, 6 or 7, then saved, after which they can be opened in Logic 8 or 9.
Ok, I'll make a note to remember that as it's something that crops up here from time to time (I'm sure it's in the FAQs ?, if not we need it there)
Logic 7.2.x is the only version pre Logic 8 that can be opened on an Intel Mac. And all Macs are currently Intel. So, to convert older files now, using a current Mac, you specifically need to use Logic 7.2.x to do the conversions from older formats.
Some are v4 and earlier. What's the possible impact?