Airport utility 6.3.4 sees my airport express but 5.6.1 doesn't
I've done a factory reset on my old style airport express. I know that I need to use airport utility 5.6.1 to configure it, but it won't show up there. However if I look under the wifi icon at the top of my Macbook I can see it there, but of course 6.3.4 won't configure it.
I have another old style AEx which shows up fine in 5.6.1. Any ideas please?
iPad 2, iOS 4.3.3