Thanks for your response. I had read about these files and about renaming the addressbook.data.previous to addressbook.data and then the problem was resolved. I couldn't find those files on my iMac.
What I maybe should add is that I had to rebuild the entourage database recently (15 Feb) and that might have screwed up my address book. I can see various addresses in my entourage address book and have also tried (unsuccessfully) to import them to Address Book.
Any further ideas? Your help is much appreciated.
Paul, get one of these...
Find Any File...
I'd get EasyFind...
Search your whole drive for...
Do we find a bigger one?