-I open my address book. I hi-light a name and click on "Send email to."
The name appears in the "TO" line of the email. Fine. But starting a couple
of days ago, when I tried to go back to the address book to copy the email to
other people, I was barred from clicking on the address book.

I must have done something to cause this but how do I undo it?

Your description is very vague and doesn't even sound like Outlook.
Clarify it. Specify your Outlook version.
The address book is not intended as the interface for starting new messages.
--
Russ Valentine
[MVP-Outlook]
"Scawsby" <(E-Mail Removed)> wrote in message
news:BB044A42-9801-44A3-B12B-(E-Mail Removed)...
> -I open my address book. I hi-light a name and click on "Send email to."
> The name appears in the "TO" line of the email. Fine. But starting a
> couple
> of days ago, when I tried to go back to the address book to copy the email
> to
> other people, I was barred from clicking on the address book.
>
> I must have done something to cause this but how do I undo it?