I run an iMac & a Macbook Pro.
Both have the same OS. 10.6.7

On the Macbook in Mail I click on a new email address and select 'add to address book' and it works, a new card is created automatically.

On the iMac I do precisely the same thing and its does NOT create a new card in Address book.

I have run Disc Utility;
I have checked Preferences on all programs - they are identical.

Anyone any thoughts ?