After many hours battle with the above I would just like to share the answer to help others with the same fate. When MS launched the April security update for OE under KB911567 this had a few side effects, one being loss of address book. This has been now acknowledged and fixed by MS under KB918766 and I can confirm it works! This info was found on click here which is a great site using simple english and even gave a program to update the registry for the above change rather than doing it yourself. The MS site doesn't say it in such a simple way! Hope this helps any others with same issue.