OK, same thing happens with the very minimal button on a blank form app. Clearly I don't know enough about Macs..... So, look a bit closer.
I have made an application bundle, it contains, down a couple if directories, a link back to my binary. So, I find, if I start from the link, it works, if I start directly from the binary, it fails. Hmm.
Anyway, my problem solved....
Macs are a funny beast, they really are !
David